HK1095613B - Regeneration of cupric etchants and recovery of copper sulfate - Google Patents

Description

Regeneration of copper etchant and recovery of copper sulfate

Technical Field

The invention relates to regeneration of a waste hydrochloric acid-based copper etchant solution. More particularly, the invention relates to the production and recovery of hydrochloric acid and copper sulfate from spent hydrochloric acid-based copper etchant solutions.

Background

Copper etching is a complex redox process in which copper is converted from a metallic state to an ionic state and an oxidizing agent is reduced. Acid solutions containing copper chloride are widely used as etching solutions in copper etching processes. Containing water, HCl and CuCl₂And an oxidizing agent is one such acid solution commonly used for etching printed circuit boards.

A typical etching process involves placing a resist pattern on a sheet of laminated copper. The masked copper laminate is then contacted with an etching solution (i.e., etchant) that dissolves the exposed copper without affecting the copper protected by the resist pattern. The etchant contains hydrochloric acid and an oxidizing agent, and typically also contains a cleaning brightener, an inhibitor, and the like. The etching process reactions that produce waste copper chloride are believed to be as follows:

reaction 1: [ CuCl ]₂+2HCl (aq)]+Cu⁰→2HCuCl_{2 (aqueous solution)}

Reaction 2: 2HCuCl_{2 (aqueous solution)}+ (oxidizing agent) → 2CuCl_{2 (aqueous solution)}

The copper etch process is typically operated in a continuous mode. Hydrochloric acid and an oxidizing agent are continuously added, and simultaneously, a waste liquid containing copper chloride is continuously discharged. Oxidizing agents used in the etching process may include, but are not limited to, hydrogen peroxide, chlorine, or sodium chlorate. The waste copper chloride produced in the copper etching process is typically transported off-site for copper recovery. According to the Resource Conservation and Recovery Act (RCRA), waste copper chloride solutions are often considered hazardous waste, which increases shipping and handling costs. In addition, the spent copper ions typically leave the process as spent brine. Due to the high cost of transporting, handling and processing these waste streams, there is much focus on-site recycling.

Various methods have been used to treat other acidic waste streams. Bandyopadhyay discloses a Treatment method for Acid group cleaning operation in the metal industry in journal of Industrial Pollution Control, 15(2), page 259-265, 1999, "Treatment of Metal Acid cleaning Waste (Treatment of Acid cleaning Waste of Metals)". Such treatment methods include neutralization, precipitation, crystallization and acid recovery. U.S. Pat. No. 3,635,664 to Morimoto discloses a method of regenerating spent hydrochloric acid pickle liquor. The method is used for FeCl in waste liquid₂Conversion to FeSO₄. Similarly, Kumar et al, Envron. Eng. Sci.15(4), pp 259-260, 1998"Recovery of Acid from Pickling Liquors" discloses a process for treating spent HCl pickle liquor to recover 85% HCl and 86.5% pure FeSO₄The method for recovering resources of (1).

U.S. patent No. 5,013,395 to Blumberg et al discloses a method of regenerating a metal-containing acid solution enhanced with salt-free materials. The metal dissolved in the acid solution is continuously oxidized by introducing gas into the packed reactor. U.S. patent No. 5,500,098 to Brown et al discloses a method and apparatus for regenerating volatile acids containing metal salt impurities. U.S. Pat. No. 5,560,838 to Allies et al discloses a method of converting an etchant to a non-hazardous substance by reaction with hot caustic (sodium hydroxide).

However, the copper-related processes are generally more complex. U.S. Pat. No. 4,604,175 to Naumov et al discloses an electrochemical reduction and oxidation (redox) process for regenerating ferric copper chloride etching solutions. U.S. Pat. No. 5,421,966 to Oxley discloses an electrolytic apparatus and method for on-line regeneration of an acidic cupric chloride etching bath. Preferred systems employ flow-through graphite or carbon anodes and flow-through cathodes to allow more precise control of current and voltage. JP 04089316 to Sakata et al discloses a method for recovering copper salts from a solution containing hydrochloric acid in which the solution is dehydrochlorinated by electrodialysis or diffusion dialysis to remove HCl. JP 11158661 to Hosoda discloses a method of extracting copper from a spent etching solution using an acid-based extraction solution and electrolyzing the copper-containing acid solution to recover the copper.

The aforementioned references have inherent problems. For example, the energy consumption associated with electrochemical or electrolytic methods for regenerating acidic etching solutions is too high. The energy and handling costs associated with other steps, such as evaporation, distillation-based processes, are also high. The transportation, handling and transportation costs associated with caustic based processes are also very high. Accordingly, there is a need for improved methods of recovering materials from copper chloride-based acid solutions, particularly for cost-effective methods of recovering usable or marketable products such as copper sulfate and hydrochloric acid from spent chloride-based copper etching solutions.

Disclosure of Invention

The spent chloride-based copper etching solution typically contains water, hydrochloric acid, and copper chloride. One of the key aspects of the present invention is to provide a method for regenerating spent etching solutions containing copper salts and thereby recovering copper sulfate and hydrochloric acid in concentrations (strength) that are easily reused in the etching process.

In one embodiment, the present invention provides a method of regenerating an etching solution comprising copper chloride. In another embodiment, the present invention provides a process for regenerating copper chloride-containing etching solutions containing spent HCl, wherein the process results in the recovery of etch-grade (e.g., hydrochloric acid of sufficient concentration and purity to be readily reused in copper etching formulations) HCl and marketable CuSO₄(i.e., it may be used in applications where technical grade copper sulfate is typically used, such as animal feed, copper powder formation, or addition to wood preservatives).

In one embodiment, the present invention provides for the incorporation of CuCl₂And HCl, the method comprising the steps of:

(a) adding sulfuric acid to the spent etching solution and adding CuCl₂Conversion to CuSO₄And HCl to provide a mixture of at least about 2 moles of sulfuric acid per mole of Cu, preferably at least about 3 moles of H per mole of copper₂SO₄Or at least 5.5 moles, e.g., from about 4 moles to about 6 moles of H per mole of copper₂SO₄Or from about 3.5 moles to about 5 moles of sulfuric acid per mole of dissolved copper;

(b) distilling the mixture from step (a) to evaporate and thereby remove substantially all, such as greater than 80 wt%, preferably greater than 90 wt%, such as 95 wt% to 99.9 wt%, of the chloride to form a vapor comprising HCl and water;

(c) condensing the vaporized HCl and water to recover hydrochloric acid, preferably wherein the hydrochloric acid is of sufficient purity and concentration to make it readily available for use in the formulation of new copper etchants;

(d) separating precipitated CuSO from excess sulfuric acid-containing residual liquid₄(ii) a And

(e) optionally, but preferably, at least a portion of the remaining liquid is reused as the sulfuric acid source in step (a). In one embodiment of the invention, the process for regenerating spent etching solution is run on a continuous basis. In another embodiment, the method is run on a batch basis.

Other compounds that may be present in the spent copper etching solution and which have appreciable vapor pressure when in a strongly acidic composition may be recovered with hydrochloric acid. An example of such a compound is hydrofluoric acid, which is a known aid in some copper etching compositions, and which can be recovered and reused in the hydrochloric acid recovery step.

In one embodiment, a pretreatment step is added whereby H is added₂SO₄The etchant is previously distilled to remove water, for example by boiling the water at a temperature preferably less than about 120 ℃, such as from about 100 to 110 ℃, and at a pressure of from about 0.8 to about 1.2 atmospheres. In one embodiment of the invention, step (a) further comprises concentrating the spent etching solution to a concentration of at least about 10, 15, 25, or 30 wt% chloride (as HCl). Generally, the higher the chloride fraction of the spent etchant, the lower the energy required to remove the chloride and form usable (especially for use as an etchant) hydrochloric acid. Compositions with higher chloride content minimize water distillation, which is advantageous because of its energy and expense. Additionally or alternatively, the water may be removed by exposing the solution to a desiccant such as anhydrous calcium sulfate (or even anhydrous copper sulfate). The substance can absorb and bind water and can be regenerated and reused many times by simple heating. Additionally or alternatively, in some cases it may be economical to add oleum, such as oleum (oleum), to step (a) in place of sulfuric acid, the function of which is to remove water.

It is important to add a substantial excess of sulfuric acid in step (a), e.g., at least about 2 moles of sulfuric acid per mole of Cu, preferably at least about 3.5 moles of H per mole of copper₂SO₄More preferably about 4.3 moles of H per mole of copper₂SO₄For example from about 3.5 moles to about 5 moles of sulfuric acid per mole of dissolved copper. Additionally or alternatively, the amount of sulfuric acid added is greater than at least about 3 moles of sulfuric acid per mole of Cu, preferably at least about 3.5 moles, and more preferably from about 4 to 5.5 moles of H per mole of Cu₂SO₄Or at least about 1 mole of sulfuric acid per 1.5 moles of chloride. Although there is no upper limit on the amount of sulfuric acid that can be used, it is not necessary to use an amount greater than about 6 moles of sulfuric acid per mole of Cu and greater than about 1 mole of sulfuric acid per 1 mole of chloride. Furthermore, because the vessel would be too large, and because the acid must be heated during distillation and recovery of hydrochloric acid therefrom, the addition of a large excess of sulfuric acid is undesirable. The heat of mixing the sulfuric acid with the spent copper etchant will generate heat that can be used to raise the temperature of the composition to, or nearly to, the distillation temperature if a large excess of sulfuric acid is not used. In embodiments where the copper concentration is high (e.g., greater than about 30 grams per liter), the addition of only a stoichiometric amount of sulfate as sulfuric acid (e.g., the greater of 1 mole of sulfuric acid per mole of dissolved copper, or 1 mole of sulfuric acid per 2 moles of chloride that is not HCl) will form a slurry or solid upon addition of the acid. It will then be difficult to distill off the hydrochloric acid and/or separate the solids from the entrained liquid, and the slurry will not age the crystals in strong acid to remove the dissolved copper chloride inclusions, so the quality (and marketability) of the recovered copper sulfate will be poor. In one embodiment of the present invention, the composition in step (a) of the present invention contains at least about 40% by weight of sulfate (as sulfuric acid) after addition of sulfuric acid. In another embodiment, the composition in step (a) contains at least 50 wt% sulfate (calculated as sulfuric acid). In yet another embodiment, the composition in step (a) contains at least 60 wt% sulfate (calculated as sulfuric acid).

In steps (a) and (b), sulfate ions will bind to existing copper ions to form a copper sulfate precipitate. While the concentration of water present will affect whether the copper sulfate is primarily anhydrous, monohydrate, or pentahydrate, other factors, including temperature, are also important, as will be discussed below. In one embodiment of the present invention, the distillation in step (b) occurs at a temperature of less than about 135 ℃ and a pressure of equal to or less than about 1 atm. In another embodiment of the invention, the distillation in step (b) occurs at a temperature of less than about 130, 120, 110, 100, 90, 80 or 70 ℃, but advantageously occurs at a temperature of greater than about 55 ℃, and occurs at a pressure of less than about 1.5atm, typically at a pressure near atmospheric pressure (e.g., 0.9 to 1.2atm), in some cases at less than atmospheric pressure, for example less than about 0.99atm, 0.95atm, 0.9atm or 0.8atm, for example about 0.5 to 0.8 atm. These processes at different pressures and temperatures are not the same. Generally, lower temperatures can be used when lower pressures are used. However, the concentration of the recovered hydrochloric acid and the form of copper sulfate recovery depend on the temperature and pressure.

In one embodiment of the invention, the distillation in step (b) takes place at a temperature of from about 95 ℃ to about 135 ℃, for example from about 120 ℃ to about 135 ℃, or from about 120 ℃ to about 130 ℃, wherein the distillation pressure in step (b) is advantageously below about 1 atm.

The solid precipitated copper sulfate may then be separated from the residual liquid, which is typically a high concentration of sulfuric acid. Solids can be separated from liquids by simple settling and decanting. In one embodiment of the present invention, the precipitated CuSO is separated from the residual liquid containing sulfuric acid by filtration₄. In another embodiment of the present invention, the precipitated CuSO is separated from the residual liquid containing sulfuric acid by centrifugation₄. In any of the above ways, it may be advantageous to wash the solids to remove residual acid, and/or lime or other base may be added which acts as an anti-caking agent and acid neutralizer.

In one embodiment of the invention, the concentration of the recovered hydrochloric acid in step (c) is from about 5 moles/liter to about 15 moles/liter, preferably from about 8.5 moles/liter to about 12 moles/liter, for example from about 9.5 moles/liter to about 10.5 moles/liter.

In one embodiment of the invention, the spent etching solution in step (a) contains from about 1 mol Cl/liter to about 20mol Cl/liter, for example from about 2 mol Cl/liter to about 14 mol Cl/liter, advantageously from about 6 mol Cl/liter to about 12 mol Cl/liter, typically from about 4 mol Cl/liter to about 8 mol Cl/liter.

In one embodiment of the invention, CuSO₄Can be used as wood preservative. Alternatively, CuSO₄Can be used as a fungicide. In a first embodiment, CuSO₄Predominantly in the form of the pentahydrate, and in another embodiment, CuSO₄Mainly in the monohydrate form. The recovered solids may contain anhydrous copper sulfate under very stringent conditions with very little water in the liquid. Typically, the recovered CuSO₄Contains monohydrate and pentahydrate, although conditions may be varied to favor one form over another.

In one embodiment of the invention, the recovered CuSO₄Is at least 85 wt%, more preferably at least 90 wt%, most preferably from about 95 wt% to about 99 wt% copper sulfate monohydrate. In another embodiment, the recovered CuSO₄Is at least 85 wt%, more preferably at least 90 wt%, most preferably from about 95 wt% to about 99 wt% copper sulfate pentahydrate.

Drawings

In the attached drawings:

FIG. 1 is a schematic diagram of a batch mode internal recovery process;

FIG. 2 is a schematic illustration of an internal recovery process for a continuous mode; and

FIG. 3 is an illustration of the experimental setup used in examples 1-6.

Detailed Description

Unless otherwise indicated, all compositions are given in percent, where percent is by weight based on the total weight of the total composition, e.g., solution fluid, solids or slurry. Where the composition is defined as "parts" of the various components, the parts are parts by weight, and if the value is not a ratio of parts, the total number of parts in the composition is from about 90 to about 110.

According to 40 Code of Federal Regulations (CFR) § 261, spent etching solutions are generally classified as RCRA hazardous waste. Therefore, the spent etching solution must be treated both on-site and off-site in accordance with the laws and regulations of RCRA. This results in increased costs for handling, transportation, storage, disposal and general liability. One such way to minimize or eliminate these costs is the internal recovery of the spent etching solution. For example, closed loop reclamation of spent etching solution can eliminate its complete classification as hazardous waste and virtually eliminate costs due to RCRA regulations. In the case where spent etching solution cannot be avoided by closed loop recovery, internal recovery can eliminate the need for transport off-site, resulting in cost savings. In addition, internal recycling can minimize the amount of waste byproducts that must be disposed of as hazardous waste.

Internal recovery of spent etching solution is advantageous for a variety of other reasons. For example, internal recycling may eliminate the need to purchase hydrochloric acid for the etching process, as the etching-grade hydrochloric acid is regenerated in the recycling process. Internal recovery may also provide other sources including CuSO₄The inner marketable by-product, CuSO₄Can be used, for example, as a preservative for processing wood products, as livestock feed (provided that the heavy metal content is low), and/or for the manufacture of copper powder.

According to the invention, the CuCl in the waste etching solution is removed₂Conversion to HCl and CuSO₄Sulfuric acid is added to the hydrochloric acid-based spent etching solution in the necessary amount. An excess of sulfuric acid must be added, for example at least 100% excess based on moles of dissolved copper, and at least 200% excess when the concentration of dissolved copper is 20% excess by weight, typically up to about 500% excess based on moles of dissolved copper.The spent etching solution contains from about 1 mole/liter to about 20 moles/liter of total chloride, preferably from about 2 moles/liter to about 14 moles/liter of total chloride, typically from about 6 moles/liter to about 10 moles/liter of total chloride. To ensure complete reaction, the amount of sulfuric acid added is in excess of that used to dissolve CuCl₂Conversion to HCl and CuSO₄The necessary amount. The reaction may take place in a reactor or distillation column. In one embodiment of the invention, the amount of sulfuric acid in the original mixture of sulfuric acid and spent etching solution is at least 30 wt%. In another embodiment of the invention, the amount of sulfuric acid in the original mixture of sulfuric acid and spent etching solution is at least 40 wt%. In another embodiment of the invention, the amount of sulfuric acid in the original mixture of sulfuric acid and spent etching solution is at least 50 wt%. In another embodiment of the invention, the amount of sulfuric acid in the original mixture of sulfuric acid and spent etching solution is at least 60 wt%. Alternatively, the amount of sulfuric acid added is at least half the molar amount of dissolved chloride, preferably at least 1 times the molar amount of dissolved chloride, more preferably at least 2 times the molar amount of chloride.

In a subsequent process step, substantially all of the chloride in the spent etching solution is recovered as hydrochloric acid. The reaction of the spent etching solution with sulfuric acid accomplishes two tasks. First, as discussed above, it will deplete CuCl in the etching solution₂Conversion to HCl and CuSO₄. Second, it utilizes the boiling point difference between sulfuric acid (boiling point about 340 ℃) and hydrochloric acid (boiling point about 110 ℃) to achieve efficient separation of sulfuric acid from HCl/water by distillation.

In a preferred method, the mixture of spent etching solution and sulfuric acid is subjected to steam distillation at approximately atmospheric pressure (± about 0.2atm) to achieve the desired vaporization of HCl from the residual liquid. In this process, a portion of the condensed hydrochloric acid may be refluxed to the top of the reactor (or distillation column). Also in this process, the residual liquid formed contains, in addition to the sulfuric acid and CuSO typically present₄In addition, additional water is present. Can separate CuSO from sulfuric acid₄The liquid was previously fed to an evaporator to remove a portion of the water. The evaporator has an external heat source. Go outWater vapor from the evaporator enters the condenser and is discharged as a waste stream. The concentrated mixture is then fed to a separation device where the CuSO is introduced₄Separated from the sulfuric acid.

After addition of sulfuric acid, a portion of the CuSO may be separated from the residual liquid at any time₄. However, typically at least a portion of the copper will be complexed with CuClxH₂The form of O remains in the residual liquid until the hydrochloric acid is removed, so CuSO is typically added after HCl removal₄And (5) a recovery step. Furthermore, CuSO will be isolated₄After a delay to recover HCl and water, a higher purity CuSO will be produced₄With less contaminants, e.g. CuSO₄CuCl present in or on the precipitate₂. In another method, the residual mixture after HCl removal is charged to a horizontal thin film evaporator and the CuCl is added₂xnH₂Conversion of O to CuSO₄. This method eliminates the need for a separator. The device will rely on inert gas with added H₂SO₄The large surface area between the spent etchants to achieve efficient removal of HCl and some water.

In another preferred process, the mixture is subjected to flash distillation under reduced pressure. The pressure may be, for example, from about 0.7 atmospheres to about 0.99 atmospheres (absolute), preferably from about 0.85atm to about 0.95 atm.

Whether operated by steam distillation, flash distillation, or other distillation means, the reactor (or distillation column) is maintained at a temperature sufficiently high to vaporize the HCl and provide a supply of CuCl₂Conversion to CuSO₄Favorable kinetic conditions. In a preferred process employing steam distillation, such temperatures may range from about 70 ℃ to about 150 ℃, or preferably from about 100 ℃ to about 120 ℃, for example from about 105 ℃ to about 110 ℃ at approximately atmospheric pressure. In a preferred process employing flash distillation, the distillation may occur at a temperature of from 70 ℃ to 150 ℃, or preferably from 80 ℃ to 110 ℃, for example from 90 ℃ to 100 ℃.

The process may be operated in a continuous or batch mode. The elevated temperature in the reactor (or distillation column) can be achieved using a variety of techniques, including, but not limited to, the application of steam directly or indirectly to the reactor. The vapors exiting the reactor were condensed to recover hydrochloric acid. The hydrochloric acid concentration in the recovered vapor can be from about 5 moles HCl/liter to about 15 moles HCl/liter, but preferred concentrations are those that are readily available for formulating new etchants, such as from about 8.5 moles HCl/liter to about 12 moles HCl/liter, typically from 9.5 moles HCl/liter to about 10.5 moles HCl/liter. At such concentrations, the recovered HCl can be readily used to formulate new etching solutions without the need for complex concentration steps.

Generally, some time is required to recover the hydrochloric acid. Sparging the acidified composition with an inert gas such as nitrogen or air, and optionally but advantageously recovering the air after condensing out the water and hydrochloric acid in the condenser, can be used to accelerate the removal of hydrochloric acid from the composition. The addition of a substantial excess of sulfuric acid promotes the conversion of copper chloride (which may exist as dissolved ions and/or compounds complexed with multiple water molecules) to volatile hydrochloric acid and precipitated copper sulfate (in anhydrous, monohydrate, and/or pentahydrate forms). Heating and refluxing during the removal of hydrochloric acid helps to remove entrained copper chloride from the precipitated crystals. The gradual conversion and removal of copper chloride from the composition will result in a gradual reduction of copper chloride in the copper sulfate precipitate, which is present as a contaminant in the crystals, as a fluid inclusion or even a fluid wetting the copper sulfate precipitate. For this reason, it is generally preferred to remove hydrochloric acid from the composition stepwise, and it is also preferred that the copper sulfate precipitate is not separated and recovered unless the composition is substantially free of hydrochloric acid, e.g., the precipitate is contacted with the fluid until the chloride level in the fluid is advantageously reduced to less than 2 wt%, preferably less than 1 wt%, more preferably less than 0.5 wt%, based on the weight of the composition.

The resulting solution essentially containing sulfuric acid and CuSO₄The mixture is put into a separation device to separate CuSO from sulfuric acid₄. Separation may be performed by techniques including, but not limited to, filtration and centrifugation. The method may further comprise washing the precipitated CuSO₄To improve its purity. By precipitationCuSO₄Copper sulfate monohydrate, copper sulfate pentahydrate or mixtures thereof, which may be 85% pure by weight, preferably at least 90% pure, more preferably at least 98% pure. Precipitated CuSO₄Which can subsequently be used as a wood preservative. Advantageously, the recovered precipitate has a weight percent chloride (based on copper chloride) of less than about 8 weight percent, preferably less than about 4 weight percent, more preferably less than about 2 weight percent, for example from about 0.1 weight percent to about 1 weight percent (based on copper chloride). Chloride is undesirable in precipitation because chloride can promote undesirable corrosion of metal fasteners in wood treated with copper chloride-containing materials.

Recovery of hydrochloric acid and CuSO₄After separation, the residual liquid is treated to be used again as a sulfuric acid source. Often, little or no processing is required. The concentration of recovered sulfuric acid in the residual liquid can vary, but is typically in the range of 40 wt% to about 75 wt%. If the concentration is below 45%, the concentration can be easily increased by removing water, for example by distillation. A small amount of waste liquid containing a small portion of this liquid can be discarded to prevent the accumulation of salts. To compensate for losses, sulfuric acid and/or oleum may be added to the material. Concentrated sulfuric acid in an amount of about 90 wt% to about 99.9 wt% may be mixed with the recovered sulfuric acid to increase its concentration to provide sufficient sulfuric acid to mix with the spent etching solution. Oleum, such as oleum (oleum), may be added in place of a portion of the newly added sulfuric acid, especially when excess water is present.

The distillation process typically requires the addition of a large amount of thermal energy. Advantageously, the process is carried out in a manner that conserves heat. For example, sulfuric acid and copper sulfate are heated to distill off hydrochloric acid. This heat can be conserved by separating the precipitated copper sulfate from the sulfuric acid/water containing residual liquid at or near distillation temperature. The heated aqueous sulfuric acid may then be mixed with newly arriving chloride-containing spent copper etchant fluid. The latent heat of the aqueous sulfuric acid composition, plus the heat generated by mixing the aqueous acid (plus any added make-up sulfuric acid) with the spent etchant, will essentially preheat the composition to near or at the planned distillation temperature required to remove the hydrochloric acid. In addition, the heat recovered by condensing the hydrochloric acid can be used to preheat fresh spent acid. Typically, no heat exchanger is depicted in the drawings, as one of ordinary skill in the art would be able to provide an appropriate heat exchanger or the like to conserve and reuse thermal energy.

Fig. 1, 2 and 3 depict an overview of the basic elements of a continuous process (fig. 1, 3) or a batch process (fig. 2, 3). It should be recognized that there is little difference in the schematic diagrams of the most preferred embodiments of the batch and continuous process apparatus. Most of the differences are in operation.

FIG. 1 depicts an overview of a batch mode internal recovery process. Containing hydrochloric acid and CuCl₂Flows through line 101 into reactor 103 where it is mixed with concentrated sulfuric acid that enters reactor 103 through line 102. The temperature in the reactor 103 is adjusted so that CuCl can be converted into₂Conversion to CuSO₄In turn, the HCl can be vaporized, which is advantageously above about 70 ℃. The HCl vapor is directed through line 104 to condenser 105 where aqueous liquid hydrochloric acid is condensed. Although it is also desirable to remove water from the mixture, the conditions in reactor 103 should be maintained at a concentration that provides a concentration of HCl in the condensate that can be used to formulate a fresh etching solution. The residue in reactor 103 contains sulfuric acid and CuSO₄It is directed via line 106 to separator 107 where solid CuSO is separated from liquid sulfuric acid₄And (4) crystals. The sulfuric acid is then directed back to the reactor for reuse via line 108.

In the continuous process of FIG. 2, hydrochloric acid and CuCl are contained₂The spent acidic etching solution flows into reactor 202 through line 201. Optionally, the fluid is pumped, preheated, and/or water evaporated (requiring a heat source) in unit 203 and then continues to flow into the reactor via line 204. If the etchant is concentrated by removing water, the water vapor exiting via line 205 can be vented or treated. Pumping, preheating, and/or dehydration are all advantageously performed prior to mixing the etchant with the sulfuric acid provided via line 206. Reacting sulfuric acid, typically aqueous sulfuric acid, in a reactionMixing with the spent etchant in the reactor or facilitating mixing thereof in the volume just before the reactor 202. Sulfuric acid, typically aqueous sulfuric acid, is delivered to the spent etchant via line 206. The sulfuric acid/spent etchant composition next enters the reactor 202, which reactor 202 may include a distillation apparatus or tray at the top thereof. The reactor should be adapted to handle the slurry and separate the evolving water vapor and hydrochloric acid vapor out of the reactor, such as by outputting the vapor from the reactor via line 207 while outputting the aqueous sulfuric acid/copper sulfate slurry from the reactor via line 208. Thermal energy may be provided to the reactor 202, for example, by a heat exchanger 209, the heat exchanger 209 utilizing a heating fluid that enters the heat exchanger via line 210 and exits via line 211 upon providing the desired increase in thermal energy. The temperature is adjusted to enable the CuCl₂Conversion to CuSO₄In turn, the HCl can be vaporized, which is advantageously above about 70 ℃. The HCl vapor is directed to condenser 212 via line 207, which optionally includes a pump, typically a vacuum pump 213 disposed before or after condenser 212, where line 214 may be included to transport the vapor from pump 213 to condenser 212 if pump 213 is disposed between reactor 202 and condenser 212. Typically two liquid streams are withdrawn from condenser 212-the condensed recovered aqueous hydrochloric acid is withdrawn via line 215, while the non-condensables may be discharged via line 216. Generally, the location of the pump relative to the condenser will affect the quality and concentration of the aqueous hydrochloric acid recovered from the condenser 212. While it is also desirable to remove water from the mixture, the conditions in the first reactor should be maintained to provide a concentration of HCl in the condensate in line 215 that can be used to formulate a fresh etching solution. Sulfuric acid and CuSO from reactor 202₄Is directed via line 208 to an optional evaporator 217 having an outlet 218 for blowdown water vapor and a transfer line 219 to a solid/liquid separator 220. In separator 220, solid CuSO₄The crystals are separated from the liquid sulfuric acid and leave the separator via line 221 or 222. The sulfuric acid is then directed back to reactor 202 via line 206 for reuse. The separated copper sulfate solids will contain sulfuric acid, which wets the liquid and acts as an inclusion in the solids. Advantageously, in the scrubber 223 byWater is provided in line 224 to wash the solids and then to dewater them again or to output as a slurry via line 225. The aqueous wash may contain a base, such as lime, to further neutralize any residual acid. If it is desired to provide new make-up acid, it can be provided via line 226, and if a small side stream must be withdrawn to control salt accumulation, it can be withdrawn via line 222. In this steady state process, the amount of chloride in the slurry in reactor 202 is kept low to minimize copper chloride contamination of the recovered copper sulfate. The amount of copper chloride is advantageously less than 4 parts by weight, for example 0.1 to 2 parts by weight, per 100 parts of slurry in the reactor 10.

FIG. 3 depicts a small pilot plant used to generate the data in examples 1-6. Fig. 3 may also be used for batch processing, although it should be appreciated that some of the tanks required for batch processing of stored material are not shown in fig. 2 and 3. In fig. 3, a reactor (beaker) 301 is in contact with a heating plate 302 for supplying heat to a heat exchanger (water bath) 304, the water bath or heat exchanger 304 being arranged to supply heat to a reactor 305. A thermometer 303 is located in the water bath 304 to monitor the water temperature. Pump 306 is used to pump CuCl₂And sulfuric acid is pumped via line 307 to port 308 of reactor 305. The appropriate temperature in the water bath 304 and in the reactor 305 is achieved using controls on the heating plate 302. When the appropriate reaction conditions (i.e., temperature and residence time) are met, the CuCl₂Conversion to CuSO₄. At the same time, a partial vacuum is achieved in reactor 305 through port 308 to draw out HCl and water vapor. With sulphuric acid and CuSO in appropriate positions₄The mixture is recycled to allow continuous operation during the distillation reaction. Filter 313 is used in the recycle loop to separate CuSO from sulfuric acid₄And (4) crystals. Line 311 exits port 310 of reactor 305 and reenters the reactor through port 309. Pump 312 is used to pump sulfuric acid and CuSO through line 311₄And (4) recycling. Filter 313 is placed over port 309 at the end of the circulation loop. Optionally but advantageously with sulfuric acid and CuSO in place₄Circulation loop of the mixture for continuous operation during the distillation reaction to help mix the fluids and provide slurry andcontact between the vapors. The remaining equipment can be understood by operation of the equipment with similarly numbered equipment in the steady state process schematic. One difference is that copper sulfate will begin to precipitate in a slurry with a high copper chloride content, but the copper chloride content of the slurry will decrease and eventually approach zero. The first precipitate formed may be more contaminated with copper chloride than the precipitate formed later in the process. The circulation of the slurry and aging of the precipitate during the batch process can reduce the amount of cupric chloride in the precipitate formed early.

Typically, when the molar ratio of sulfate to dissolved copper in the composition fed to the reactor exceeds 3.5: 1, then the residual amount of copper in the fluid is low, e.g., less than 20 grams/liter. Generally, substantially all (> 95%) of the copper sulfate will typically precipitate when an equimolar amount of sulfate is added to the copper present. The concentration of the precipitate is therefore controlled mainly by the conditions present in the early part of the process.

The high concentration of sulfuric acid and, at the same time, the low concentration of water favor the formation of the monohydrate form of copper sulfate. If the sulfuric acid concentration is above 70 wt%, e.g., 85 wt% to 98 wt%, and the water concentration is below 28 wt%, e.g., 2 wt% to 14 wt%, then the monohydrate form of copper sulfate will predominate. The product may contain 70% by weight or more, possibly 90% by weight or more, of copper sulphate in anhydrous form (rare) and monohydrate form (more common).

The medium concentration of sulfuric acid and simultaneously the medium concentration of water favours the formation of copper sulfate in the pentahydrate form. If the concentration of sulfuric acid is about 50 wt%, such as about 40 wt% to 55 wt%, and the concentration of water is greater than 25 wt%, such as 30 wt% to 40 wt%, then copper sulfate in the pentahydrate form will predominate. The product may typically contain 40 to 80 wt% copper sulfate in the pentahydrate form, and rarely above 80 wt% copper sulfate in the pentahydrate form.

Although it is possible to make a product with copper sulfate in the pentahydrate form above 80 wt%, such compositions typically contain too much water, making the recovered hydrochloric acid concentration too low to be suitable for use in making new etchants unless there is also an energy intensive concentrator process step to partially dehydrate the spent etchant. Energy consumption is more advantageous when the amount of water in the composition is kept low. Thus, in the most preferred embodiment of the invention, the preferred product is copper sulfate in the monohydrate form. However, if the spent etchant contains a large amount of water, it is often advantageous to try to provide a product that is primarily copper sulfate pentahydrate.

In most commercial processes, the product will contain a significant portion of copper sulfate monohydrate and copper sulfate pentahydrate, for example, greater than 20 mole percent copper sulfate monohydrate and copper sulfate pentahydrate. This will not cause any problems if the end-use application, for example the preparation of wood preservatives for fungicides for foliar application, does not depend on the purity of each other.

The process of the present invention is illustrated by the following examples, which are merely illustrative of the nature of the invention and should not be construed to limit the scope of the invention or the scope of the appended claims in any way.

Example 1

25ml of a copper chloride solution containing 129-g/L copper and 65-g/L HCl was mixed with 31.3 grams of concentrated sulfuric acid (97 wt% sulfuric acid). The aqueous composition contains about 0.066 moles of copper, 0.177 moles of chloride and 0.31 moles of sulfuric acid. The mixture solution, initially containing about 50 wt% sulfuric acid and about 35 wt% water, was distilled under a slight vacuum (using a water pump) at 130 ℃ for 35 minutes. After distillation a light blue solution/crystal mixture was obtained. The mixture was allowed to cool down and then filtered. About 25-ml of filtrate and 9.7 grams of light blue copper sulfate crystals were collected. After drying in an oven at 50 ℃ overnight, the crystals (formed from a composition having a sulfate to copper molar ratio of about 4.7: 1, about 50% sulfuric acid, and about 35% water at 130 ℃) were found to contain 28.3% copper, 1.5% sulfuric acid, and 0.5% free moisture. The filtrate contained 2.37-g/L chloride and 15-g/L copper, and had a specific gravity of 1.51 g/cc. During the distillation, condensate was partially collected and contained 196-g/L HCl or about 5.3 moles HCl/L. The mass balance indicates material loss during the process. However, 15g/L of dissolved copper residue indicated more than 80 of copper precipitated. Since copper sulfate monohydrate contains 35.8 wt% copper and copper sulfate pentahydrate contains 25.4 wt% copper, a composition with a copper content of 34.8% would be expected to contain 90 mol% monohydrate and 10 mol% pentahydrate; a composition with a copper content of 30.6% would be expected to contain 50 mol% monohydrate and 50 mol% pentahydrate; a composition with a copper content of 28% would be expected to contain 25 mol% monohydrate and 75 mol% pentahydrate. The precipitate recovered from this experiment contained 28.3% Cu, indicating that the material had about 2.5 parts copper sulfate monohydrate per 7.5 parts copper sulfate pentahydrate.

Example 2

A mixture of 30ml of copper chloride solution (245.4-g/L copper (from cupric chloride) and 35-g/L HCl, density 1.407g/cc) and 42.2g sulfuric acid was distilled under a low vacuum at 120 ℃ for 35 minutes. The composition initially contained 0.116 moles Cu, 0.26 moles Cl and 0.41 moles H₂SO₄. About 26 grams of copper sulfate crystals and 38 grams of filtrate were obtained. The crystals contained 28.1% copper, again indicating that the material had about 2.5 parts copper sulfate monohydrate per 7.5 parts copper sulfate pentahydrate. The filtrate was a pale blue solution containing 72.6% by weight of sulfuric acid and 5g/L of copper, and had a specific gravity of 1.33 g/cc. The copper recovery was about 90% based on copper sulfate.

Example 3

A mixture of 42.2ml of copper chloride solution (245.4-g/L copper and 35-g/L HCl, density 1.407g/cc) and 21.1g of sulfuric acid was distilled under a low vacuum at 125 deg.C for 60 minutes. The composition initially contained 0.163 moles of Cu, 0.366 moles of Cl and 0.209 moles of sulfuric acid. The initial mixture solution contained about 33 wt% sulfuric acid. After distillation, a light blue concentrated solution was obtained. Upon cooling, the liquid crystallized to form light blue copper sulfate crystals. The filtrate was not recovered. The material may contain about 20% by weight sulfuric acid that is not readily separated from the solids.

Example 4

The reactor was first charged with 400ml of a solution containing 93 wt% sulfuric acid. The solution was stirred and heated to 85 ± 5 ℃. Copper chloride (134.1g/L copper, 65g/L HCl) was started and maintained at a constant rate of 2 ml/min. About 100ml of concentrated sulfuric acid was added to the reactor for every 300ml of cupric chloride solution added. During the distillation reaction, copper sulfate crystals were formed and continuously removed through a filter funnel installed at the top of the reactor. After a total of 900ml of cupric chloride and 300ml of sulfuric acid solution were added, the total solution volume reached a steady state of about 600 ml. The liquid contained about 70 wt% sulfuric acid and 5g/L copper. The resulting copper sulfate crystals were light blue in color. The unwashed crystals contained 35% copper and 8.1% sulfuric acid. This indicates that the material has about 9 parts copper sulfate monohydrate per part copper sulfate pentahydrate. About 8.5 moles of sulfuric acid, 5.4 moles of Cl, 1.9 moles of Cu, and 49 moles of water were added together in the reactor. The copper recovery rate is higher than 97%.

Example 5

Water was added to the reaction residue of example 5 to dilute the sulfuric acid concentration to about 50%. The copper chloride solution was added to the reactor at a rate of 2 ml/min. No further sulfuric acid was added. The distillation temperature was maintained at about 85. + -. 5 ℃. Samples of the solution and copper sulfate crystals were taken at several stages of copper chloride addition. The results are shown in the following table.

During the addition of cupric chloride, the sulfuric acid in the reaction heel was continuously consumed, but was maintained at an approximately steady state concentration of 50%. This indicates that the evaporation rate is faster than 2ml/min with copper chloride added, but care must be taken with the data. When the sulfuric acid was maintained at about 70 wt%, crystals containing about 35% copper were recovered. While the sulfuric acid was maintained at about 50 wt% sulfuric acid, the copper content of the recovered crystals was reduced to 30.4% (indicating a mixture of about 1 part by weight copper sulfate monohydrate and 1 part by weight copper sulfate pentahydrate). An increase in the sulfuric acid content to 55 wt% correlates with an increase in the copper content of the crystals to 31.9% (indicating a mixture of about 6 parts by weight copper sulfate monohydrate and 4 parts by weight copper sulfate pentahydrate).

Example 6

Firstly, the reactor is filled with150ml of concentrated sulfuric acid (98%) are added. The solution was stirred and heated to 85 ± 5 ℃. Copper chloride (134.1g/L copper, 65g/L HCl) was started and maintained at a constant rate of 2 ml/min. After the addition of 200ml of the copper chloride solution was complete, the distillation reaction was allowed to continue for about 30 minutes before the copper sulfate crystals were separated from the solution. During this test, the composition in the reactor was constantly changing, with initial copper sulfate precipitation occurring from a composition containing more than 95% sulfuric acid and very little water, and final copper sulfate precipitation occurring from a composition containing about 60% sulfuric acid and about 39% water. To the initially charged 1.84 moles of sulfuric acid, 0.42 moles of Cu and 1.2 moles of Cl were finally added. H₂SO₄The final concentration of (c) is 60%. The mass balance in this experiment is given below.

Item	Copper, g	HSO，g	Chloride, g
					Feeding material	26.82	269	42.6	850.2
Output stream crystal filtrate NaOH scrubber totaled	23.543.000.026.54	38.3213.8-218.6	0.030.2142.3942.6	73.2355.5372.7801.4
					Percent recovery rate%	99.0	93.7	100	94.3

^*This assumes that there are 2 moles of copper sulfate monohydrate per mole of copper sulfate pentahydrate in the recovered crystals, making this material about 49% sulfate. The copper sulfate monohydrate form contains 54 wt% sulfate, while the copper sulfate pentahydrate contains 38 wt% sulfate.

The solid separation was carried out in a filter funnel and the crystals were not washed with water. The copper sulfate crystals weighed about 73.2g and contained 32.17% copper and 6.61% sulfuric acid. The copper sulfate material may contain 2 moles of monohydrate form per mole of pentahydrate form. About 236ml (355.5 g) of filtrate was collected. The filtrate contained 12.7g/L copper, 906g/L sulfuric acid and 0.869g/L chloride. During the distillation, a caustic solution (325.7g, 23.9%) was used to absorb the hydrochloric acid vapor.

Most ingredients have an excellent mass balance. A total of about 200ml of copper chloride solution was added to the composition. The filtrate contained about 140 grams of water, so the vapor contained approximately equal weights of water and hydrochloric acid, indicating that if the vapor were condensed, concentrated (-38%) hydrochloric acid would be recovered.

The present invention is to be illustrated by, but not limited to, these examples.

Claims (29)

1. A method for regenerating a spent etching solution containing dissolved copper chloride, the method comprising the steps of:

(a) providing a spent etchant containing at least 10 wt% chloride and at least 5% dissolved copper;

(b) adding sulfuric acid corresponding to at least 2 moles of dissolved copper per mole of dissolved copper to said spent etching solution, thereby converting copper chloride to hydrochloric acid and precipitated copper sulfate;

(c) distilling the mixture obtained in step (b) to vaporize at least part of the hydrochloric acid;

(d) condensing at least a portion of the vaporized hydrochloric acid;

(e) separating at least a portion of the precipitated copper sulfate from a residual liquid, wherein said residual liquid comprises sulfuric acid; and

(f) reusing at least a portion of the residual liquid as a sulfuric acid source in step (b).

2. The process of claim 1, wherein the process is run on a continuous basis, and wherein the spent etchant, sulfuric acid, or both further contain at least 1 mole of water per mole of dissolved copper in the spent etchant.

3. The method of claim 1, wherein the method is run on a batch basis, and wherein the spent etchant, sulfuric acid, or both further contain at least 1 mole of water per mole of dissolved copper in the spent etchant.

4. The method of claim 1, wherein the amount of sulfuric acid added is at least 3 moles of sulfuric acid per mole of dissolved copper in the spent etchant.

5. The method of claim 1, wherein the amount of sulfuric acid added is at least 3.5 moles of sulfuric acid per mole of dissolved copper in the spent etchant.

6. The method of claim 1, wherein the amount of sulfuric acid added is 4 to 6 moles of sulfuric acid per mole of dissolved copper in the spent etchant.

7. The method of claim 1, wherein the amount of sulfuric acid added is 3.5 to 5 moles of sulfuric acid per mole of dissolved copper in the spent etchant.

8. The method of claim 1, wherein at least 4 parts by weight of sulfuric acid is added per 6 parts by weight of spent etchant.

9. The method of claim 1, wherein at least 5 parts by weight of sulfuric acid is added per 5 parts by weight of spent etchant.

10. The method of claim 1, wherein at least 6 parts by weight of sulfuric acid is added per 4 parts by weight of spent etchant.

11. The process of claim 1, wherein the distilling in step (c) occurs at a temperature of 95 ℃ to 135 ℃.

12. The process of claim 1, wherein the distilling in step (c) occurs at a temperature of 120 ℃ to 135 ℃.

13. The process of claim 1, wherein the distillation in step (c) occurs at a pressure of less than 1 atm.

14. The process of claim 13, wherein the distilling in step (c) occurs at a pressure of 0.7atm to 0.99 atm.

15. The process of claim 1, wherein the separated copper sulfate contains a residual liquid, the process further comprising contacting the separated copper sulfate with a base to neutralize at least a portion of the sulfuric acid in the residual liquid that is contacted with the separated copper sulfate.

16. The process of claim 1, wherein the precipitated copper sulfate is separated from the residual liquid comprising sulfuric acid by centrifugation.

17. The method of claim 1, wherein the recovered hydrochloric acid contains at least 8 moles of hydrochloric acid per liter, further comprising the step of formulating at least a portion of the condensed hydrochloric acid into a copper etchant.

18. The method of claim 1, wherein the spent etching solution in step (a) contains a total of 4 to 8 moles of chloride per liter.

19. The method of claim 1, wherein step (a) further comprises concentrating the spent etchant to at least 20 wt% chloride.

20. The method of claim 1, wherein step (a) further comprises concentrating the spent etching solution to provide a spent etchant containing at least 30 wt% chloride.

21. The process of claim 1, wherein the separated copper sulfate comprises at least 90% by weight copper sulfate pentahydrate and/or copper sulfate monohydrate.

22. The process of claim 21, wherein greater than 60 mol% of the separated copper sulfate comprises copper sulfate pentahydrate.

23. The process of claim 21, wherein greater than 60 mol% of the separated copper sulfate comprises copper sulfate monohydrate.

24. The process of claim 21, wherein greater than 80 mol% of the separated copper sulfate comprises copper sulfate monohydrate.

25. The method of claim 1 further comprising the step of converting at least a portion of the separated copper sulfate into a form in which the copper can be injected into wood, and injecting the copper into the wood as a wood preservative.

26. The method of claim 1, further comprising the step of converting at least a portion of the separated copper sulfate into a fungicidal composition.

27. The process of claim 1 further comprising the step of washing the separated copper sulfate to further remove residual liquid.

28. The method of claim 1, wherein the composition containing the reaction product of spent etchant and sulfuric acid is steam distilled to vaporize greater than 98% of the chloride in the composition as hydrochloric acid.

29. The method of claim 1 wherein at least 90 wt% of the Cu in the spent etchant is recovered as separated copper sulfate.