WO2001034523A1

WO2001034523A1 - Treatment of contaminated waste water

Info

Publication number: WO2001034523A1
Application number: PCT/US1999/026345
Authority: WO
Inventors: Stephen Ray Wurzburger; James Michael Overton
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-11-06
Filing date: 1999-11-06
Publication date: 2001-05-17
Anticipated expiration: 2002-05-06
Also published as: AU2473400A

Abstract

A method and apparatus for removing a group of species of metal ions from an aqueous solution to be purified which involves the steps for each species in succession of (1) adjusting the pH of the aqueous solution to a value where hydroxide precipitates of said species in its highest valency state are insoluble, then (2) passing the aqueous solution through an ion state modification cell in the presence of a magnetic field to raise the valence of the respective species to its highest valency state and (3) digesting the ion specie so as to form the insoluble hydroxide, then (4) removing the precipitated hydroxide from the aqueous solution by appropriate steps of settling and press filtering (5) then repeating steps (1) through (4) at a higher voltage in the ion state modification step. The magnetic field imposed between the electrodes improves the efficiency of the ion state modification step.

Description

TREATMENT OF CONTAMINATED WASTE WATER

TECHNICAL FIELD

This invention relates to a method and process for the removal of contaminants such as heavy or light metals from waste water, particularly such are discharged from various processing operations and particularly to a method which incorporates magnetic, electrolytic and chemical techniques.

BACKGROUND

There have been many attempts at the removal of light and heavy metals from aqueous solutions. These attempts include electrowhinning, reverse osmosis, electrophoresis, hydoxide precipitation, radical pH shifting, and direct chemical replacement reaction systems. All of these systems are effective only within very narrow and restrictive, process specifications

and parameters. The presence of very high large or vey small contamiant levels, the presence of large calcium levels or high pH conditions together with multivalent or multiple contaminants can completely defeat the effectiveness and applicability of the processes.

Techniques disclosed in the patent literature can generally be classified into five groups: Electrolytic; Hydroxide precipitation; Oxidation state modification; Low voltage electrolysis, High voltage electrolysis.

U. S. Patent 3,901,781 to Passino et al discloses pretreatment of water utilizing ion exchange followed by a dialysis process. Ion exchange resins are expensive and must be periodically reconditioned.

U. S. Patent 4,006,067 to Gussack discloses a process for changing the oxidation state of a dissolved ionic species using porous electrodes. Porous electrodes are subject to degradation by accumulation of scum in pores.

U. S. Patent 4,011,151 to Ho et al discloses a processs for purifying water in two steps. In the first step, the electrolysis is effected by dipping an iron anode and a carbon cathode in the waste water, filtering the water, adjusting the pH to 14 by electrolysis with a carbon

anode and an aluminum electrode.

U. S. Patent 4,054,516 to Iziumi et al discloses the use of blowing air into the solution to create a foam to carry off precipitates. This approach is not readily adaptable to processing large quantities of water.

U. S. Patent 4,121,991 to Miller et al discloses an electiOlytic treatment of water using abrasion of the anode surface with prcipitates to clean the electrrode surface. This method would be expensive to implement.

U. S. patent 4,132,622 to Kenny discloses a bi-polar cell.having a large surface area .

U. S. Patent 4,123,339 to Gale et al discloses a plurality of closely spaced parallel electrodes, using hydrochloric acid cleaning system to keep the iron electrodes free from oxides coating. Removal of the chloride ions requires an additional step.

U. S. Patent 4,338,178 to Vyacheslav et al discloses a nozzle which, together with gas formed on the surface of the electrode carry the sludge away from the electrodes.

U. S. Patent 4,566,975 to Ailgulia discloses hydroxide coprecipitation.. This approach requires the additional steps of removing and disposing of the precipitating agent.

U. S. patent 4,655,895 to Feofanov et al discloses dissolving a metal anode in the presence of a nonsoluble cathode and precipitating nonsoluble inorganic and organic impurities, the electrodes being alternately brought into contact with the air, oxygen and liquor being treated. The patent clearly states that calcium is a problem and requires a preprocessing step not disclosed. A magnetic field is positioned to remove iron particl;es.

U. S. Patent 4,676,878 to Chez discloses hydrolysis of water using a large field.

U. S. patent 4,810,344 to Okazaki discloses a plurality of electrolysis vessels, each having an anode and cathode and an electrolysis diaphragm partitioning the space between them with an alkaline water discharge conduit connected to the cathode side and an acidic discharge conduit connected to the anode side of the diaphragm. A magnetic supply unit may be disposed to the vessels to exert a magnetic effect. A diaphragm tends to have a limited life in the field.

U. S. Patent 5,045,214 to Walker discloses coprecipitating non-volatile contaminants with a carrier precipitate formed in situ in the solution. This system is essentially a batch process and requires long treatment times. The primary drawback of this type of system is that, as contaminant levels decrease, the law of "Mass Action" predicts a slowing of the reactions then takes place in these batch processes.

For example, the data presented shows a final concentration of Se to be 22 mg/1 of Se in water which issignificantly greater than the levels permitted by the present EPA Water Standard for Se allowance which is 0.05 mg/1

The processes disclosed in the cited art are not as efficient as the present invention for decontaminating the solutions having the wide range of contaminant concentrations and conditions for which the present invention is targeted nor are they practical for use in reducing pollutant ion concentrations down to the very low levels required for most solution disposal purposes.

In some instances even very low levels of contaminating materials can be a significant problem. Certain metals can cause severe damage to animal life. It is well known that the selenium level in water entering Kesterson reservoir has had a devestating effect on wildlife living in the wetlands.

The most plentiful ionic species of metallic selenium in aqueous solution is a +4 valent ion, a strong reducing agent that readily combines with oxygen to form Seθ2, a colorless solid that is readily soluble in water.

The ineffectiveness of the cited art for dealkalinizing highly concentrated solutions can be explained by considering the nature of hydrolysis.

Hydrolysis of water is the disassociation of the water molecule into ions.

The disassociation is given by:

H₂O 2H+ + (OH)-

for "cation" hydrolysis:

M+ + H₂O = M(OH) + H+

and for "anion" hydrolysis,

X- + H₂O = HX + (OH)-

While most metals and metalloids will readily form hydrated oxides and hydroxides that, in the presence of a high pH environment, precipitate out of solution, many of these "high pH precipitates" become highly water soluble upon lowering the pH level and, in doing so, recontaminate the treated water solution.

The best known example of ion state modification occurs in electroplating processes where a metal is removed from the anode and enters solution by removing an electron (oxidation) and then deposited on the cathode by combining with an electron supplied by the cathode (reduction). The electroplating process is dramatic illustration of the dependence of the solubility of an atom on the ion state. Ion state modification has been overlooked in the cited art with a consequent limitation on the effectiveness of the processes of the present state of the art.

DISCLOSURE OF INVENTION

Accordingly, it is an object of this invention to remove contaminating heavy and light metal ions from waste water and particularly to provide an efficient process for removing large concentrations of calcium and magnesium such as are found in desert waters in brines created from operations used in processing olives.

It is a particular object of this invention to remove from water impurities such as selenium and arsenic (metallic and non metallic forms) which pose a hazard even when present in small concentrations.

In comparison with prior methods of treatment of spent processing solutions, it is an object that the method and apparatus of the present invention be less complex in terms of required steps and additives required and consequently less costly. This invention is directed toward a process of steps including putting the solution through "ion state modification " chambers where ions that would normally and naturally form soluble hydroxides are converted to species that form insoluble hydroxides.

Exemplary steps of the method include:

preparation of a treatment solution containing a high concentration of hydroxyl ions;

/ mixing the waste water with the treatment fluid preferably in the presence of a magnetic field;

passing the mixture between the electrodes of at least one low voltage ionization state modifying cell wherein a magnetic field is imposed in the cell;

passing the mixture through a clarifier during which step, calcium is removed by settling and filtering;

adding a second solution containing a large concentration of hydroxyl ions preferably in the presence of a magnetic field;

passing the mixture between the electrodes of at least another one high voltage ionization state modifying cell wherein a magnetic field is imposed in the cell; clarifying the mixture by settling and drawing off Magnesium Hydroxide.

A significant feature of the invention is the enhancement of the ion state modification step by the impositon of the magnetic field on the solution while it is undergoing treatment between the electrodes of the ion state modification cell. Another significant feature of the invention is the selection of the appropriate electrodes and voltage applied between the electrodes of the ion state modification cell such as to raise the valence to a value where the resultant hydroxide formed is more insoluble.

BRIEF DESCRIPTION OF THE FIGURES:

Fig. 1 shows the steps in the process of this invention. Fig. 2 shows the steps for preparing the first chemical agent. Fig. 3 shows the apparatus for carrying out the invention.

BEST MODE FOR CARRYING OUT THE INVENTION:

Turning now to a discussion of the drawings, Fig. 1 shows the steps in carrying out the process of this invention for removing contaminating metal ions from aqueous waste solutions, particularly magnesium and calcium from brines. In step 1, a first chemical agent is added to the aqueous waste water to be purified and mixed in the presence of a magnetic field in a sufficient amount to raise the pH to about 7.5 to about 9.5 depending on the level of calcium contamination. A preferred first agent is prepared according to steps listed in following paragraphs.

In step 2, the mixture is passed serially through at least one "ion state modification" cell. Each cell has a pair of electrodes, across which an electric field is applied. The voltage between the electrodes in each cell is selected to induce change of valency of the ions.

A principle result of step 2 is to cause the precipitaion of ions such as Ca having a low ionization potential. Although I do not wish to be bound by theory, it is believed that, in this step, the Ca+÷ is converted to Ca⁺⁺⁺ by the reaction:

2 Ca⁺⁺ + 6H₂O 2Ca⁺⁺⁺ + 6(OH)- + 3H₂

In step 3, the mixture is allowed to digest so that a sludge of Ca(OH)3 forms.

In step 4, the metal hydroxide sludge (often calcium) is drawn out by settling and/or filtering and the sludge is further dewatered by passage through a filter press. At this point in the process most light metal ions that might have originally been in the waste water have been removed. In step 5 steps 1 through 4 are repeated. Mg (OH)₂ is typically used to adjust pH and mixed into the solution, preferably in the presence of a magnetic field. The "ion state modification" cell is operated at 78 to 82 volts where the Mg is oxidized according to the reaction:

2 Mg⁺⁺ + 6H₂O 2Mg⁺⁺⁺ + 6 (OH)" + 3 H₂

and the Mg⁺⁺⁺ forms large crystal of insoluble Mg(OH)3 precipitate with most heavy metal ions that might originally have been in the water and which are easily filtered out in the final step.

Fig. 2 shows the steps for preparing the first chemical agent applied in step 1.

In step 1, 40 ml of concentrated sulfuric acid (Be 12°) is added to one liter of water.

In step 2, Ca(OH)₂ is added to bring the solution up to a range of 12.1 to 13.1.

In step 3, the solution is passed through an eleven micron filter thereby removing any CaSO₄ precipitates larger than eleven microns.

In step 4, sufficient potassium hydroxide is added to bring the pH to a range of 13.8 to 14 thereby producing a base solution. In step 5, magnesia is added in the amount of 10 grams per one liter of base solution thereby formulating the first chemical agent.

Fig. 3 shows a schematic diagram of the apparatus for performing the steps of the process. There is shown an inlet for discharging the waste water into a chemical mixer 12. In one embodiment, the mixer 12 is subject to a magnetic field provided by a magnet 14. The first chemical agent is admitted to the mixer 12 from reservoir 16. The solution is allowed to digest and is then passed through two series connected "ion state modification cells" 17 and 18. Each cell has a pair of electrodes across which pair a voltage is impressed from power supply 20. The electtodes are preferably tin .The cells are preferably subjected to a magnetic field imposed by externally positioned magnets 15. The calcium and light metal hydroxides precipitate out and these precipitates are removed in the clarifier 22. The solution is then passed to a chemical mixer 24 where it is mixed with Mg(OH)₂ from reservoir 26. The solution is then passed through another "ion state modification" cell 27 where Mg(OH)3 is formed, the electrodes of the second stage cell are preferably iron,, carbon or titanium. . This precipitate is filtered out in the clarifier 30. The power supply 28 for applying power to the "ions state modification" cell 27 is shown.

The process of this invention overcomes a problem encountered in using Ca(OH)₂ in state of the art processes to raise the pH to a value high enough to precipitate metal hydroxide precipitates The problem is that the Ca(OH)₂ precipitates thus formed have very low density and consequently poor properties for filtering. U. S. Patent 4,054,516 very plainly shows that a solution of Cu-Zn mixture can be removed by adjusting the pH to 9⁺ whereas a five metal mixture of Cu-Ni-Pb- Co-Mn ions requires a pH above 10.5 to remove the ions. However a solution with a pH above 10.5 requires an excessive amount of acid for reducing the liquid back to 7.0 to 8.0 range required for dumping. The amount of cations added to the waste water for pH reduction may render the water unfit for dumping. The present invention overcomes this problem by converting the Ca⁺⁺ to Ca⁺⁺⁺ in the first two ion state modification cells as discussed above.

Magnesium hydroxide {Mg(OH)₂ is also used for water treatment in state of the art processes. Mg(OH)₂ has several advantages in that it is not a toxic metal and it has excellent filtering characteristics in terms of the its coagulant properties. However, this hydroxide is not effective for removing multiple metals primarily because it is self buffering in a pH range of 9.0 to 9.2. The present invention overcomes this problem by converting the Mg(OH)₂ to Mg(OH)3 in the third "ion state modification " cell discussed above. With the problem calcium removed, the magnesium ions are converted from Mg⁺÷ to Mg⁺⁺⁺ in the ion state modification cell using iron, titanium or carbon electrodes. The Mg(OH)3 is self flocculating and does not require additive chemical flocculating agents for precipitation and filtering.

If the treated solution is to be dumped or disposed of under the Clean Water Act, the pH needs to be reduced to a pH range from 7.0 to 8.2. The pH may be reduced using a strong acid. EXAMPLE I. A sample of contaminated cooling tower water was obtained from a Mojave Desert industrial site. The contaminants include significant amounts of Cr, Cu, and Zn and as such constitute a toxic hazard that requires treatment as a toxic waste material.

A 650 ml of sample was placed in a stage one reactor (tin anodes) and was treated for two minutes. After the initial treatment, the sample was allowed a digestion time of 2 hours. A 50 ml sub sample was taken from the initial sample and sent to a certified lab for analysis. The remainder was treated in a stage 2 laboratory "ion state modification" cell for an additional one min with no additional digestion time. Total treatment time (including time for digestion) was 2 hr. 4 min. Table I summarizes results of the above procedure:

TABLE I (concentrations expressed in ppm at different process stages) pH Ca Mg Cr Cu Zn

Untreated 6.4 140 35 0,15 0.25 0.14

Stage 1 + digestion 8.3 6.0 24.0 < 0.05 0.01 0.03

Stage 1 and 2 + digest 11.6 0.05 0.1 <0.05 <0.01 0.03

% metal reduction 99.99% 99.99% 66% 96% 79% The results of this process evaluation indicate that the process significantly reduced the levels of alkali earth and heavy metals dissolved in the tested sample to acceptable EPA levels.

EXAMPLE II

A sample of contaminated water was taken from a Mojave desert industrial site. The water from which the sample was obtained was used in steam generation as well as in a cooling water application. A small amount of HCl had been added as an algicide. The combination of silicates and arsenic together posed a major disposal problem.

A 650 ml sample was placed in a stage 1 cell and was treated for four minutes After the initial treatment the sample was allowed to digest for 1 hour. A 50 ml sub sample was taken from the the initial sample and sent to a certified laboratory for analysis. The remainder (approximately 600 ml) was treated in a stage 2 "ion state modification cell" for an additional one minute with no additional digestion time. Total treatment time was therefore 1 hr, 5 min. Table 2 summarizes the results of the above procedure.

TABLE II. ( concentrations expressed in ppm at different process stages)

Untreated 6.5 35.0 13.0 0.22 6.3

stage 1 + digest. 7.6 3.9 13.0 <0.14 3.8

stage 2 no digest 7.8 2.4 0.2 <.05 1.4

% metal reduction 93,2% 98.5 78.3 88

End stage 3 Not detectable Not detectable Not detectable 0.20

End stage 4 Not detectable Not detectable Not detectable 0.10

The results listed in TABLE II of this process evaluation indicate that the process significantly reduced the levels of alkali earth and heavy metals dissolved in the test sample. By the addition of a third and fourth treatment cells for the water soluble silicates, each having a pair of tin electrodes as discussed above, the Arsenic levels were further reduced. (See End stages 3 and 4 in TABLE II. )

Total treatment time for all four stages was 1 hr. 15 min.

EXAMPLE III.

A sample of contaminated water was taken from a well on a Northern California industrial site. The site has been in continuous service for over 40 years. The sample was highly alkaline and contained a measurable concentration of several heavy metal contaminants.

A 650 ml sample was placed in a stage one cell and treated for 4 min after which a 25 ml sample was extracted. The sample was allowed a digestion time of 1 hour. A second 25 ml sample was taken. Both extracted samples were sent to a certified lab for analysis. The remainder was placed in a stage two laboratory cell and treated for an additional minute with no additional digestion time. Total treatment time (including digestion time ) was 1 hour 5 min. TABLE III summarizes the results of the treatment.

TABLE in.

( concentrations expressed in ppm at different process stages)

pH Ca Mg Mfl Zn

Untreated 7.8 115.0 90.0 0.02 0.26

Stage 1 + digestion 8.8 6.8 80.0 0.01 0.09

Stage 1 and 2 + digest. 9.3 4.5 2.8 <0.01 0.06

% metal reduction 97 97 50 77

The results of this process evaluation show that the process significantly reduced concentration of low level contaminants as well as larger levels of contaminants. The process does not discriminate against low level contaminants.

EXAMPLE IV

Selenium exhibits multiple valence states -2, +4, +6. The multi valence selenium as a contaminant requires a multistage ion state modification cell to deal with the multiple ionic states that are present. The initial treatment is accomplished using two cells. The stage 1 cell leaves residual electrode material in the solution. The stage 2 cell is used to remove the residual stage 1 electrode material from the solution and naturally occurring magnesium. This resulted in a significant reduction of selenium levels. Results of the treatment are presented in TABLE IV.

TABLE IV. ( concentrations expressed in ppm at different process stages)

Selenium Concentration

Starting Kesterson Water 0.015

2 ea. ion state mod +

1 ea. stage 2 « 0.01

We have found that water with high Ca content is particularly immune to the most rigorous efforts to remove Se unless the Ca is not taken out first. Therefore, an embodiment of this invention includes a preparatory step of removing Ca by any of the procedures discussed above in situations where the presence of Ca requires such a step. EXAMPLE V A waste effluent was obtained from a circuit board and electroplating operation in Northern California. The solution was analyzed and the primary constituent was determined to be copper, but in multiple oxidation states. The predominant species was Cu⁺⁺ with lower levels of Cu⁺.

In order to facilitate electrode maintenance, increase effective plate area and decrease costs, a long ion state modification cell was constructed. The cell was essentially a parallel plate reaction chamber (trough) with iron electrodes which modified the Cu⁺ oxidation state to Cu⁺⁺ oxidation state prior to passing thr solution through laboratory cells which are more costly and less simple to maintain. The pH was then raised to neutral ( 7.0 + 0.5 ) by the addition of bicarbonate of soda The concenration was again analyzed and found to contain 1130 ppm copper. The treatment time in the laboratory cell was 15 minutes. During the 15 minute period, considerable precipitate formed. The copper collected during the operation was collected as "metallic copper concentrate" and was commercially maiketable as a high grade ore concentrate.

The spent etching solution was analyzed and found to contain 1800 ppm copper. Initial processing modified the Cu⁺ state to CU++. The pH shift was achieved by the addition of bicarbonate of soda. The solution was now allowed 1 hr of undisturbed digestion time. An additional drop in copper concentration to 920 ppm was observed. The solution was allowed an additional 1 hr digestion resulting in a further reduction of Cu to 910 ppm. The results are summarized in TABLE VA TABLE V.A

Initial starting cone. 1800 ppm Cone after trough treatment, filtration and pH normalization 1130.

One hr undisturbed digestion time 920

Two hr undisturbed digestion time 910

650 ml of this pretreated solution was placed in a stage 1 cell, and subjected to 4 min. treatment. Analysis indicated that Cu concentration had decreased to 300 ppm.

The solution was allowed to digest for one hr and again analyzed. The copper level had decreased further to 120 ppm. The filtrate at this point was high grade copper ore having commercial value.

The remaining solution was then put through a cell having iron electrodes for a period of 1 min. The residue was filtered and sample analyzed, the concentration had dropped to 0.59 ppm. The results are summarized in TABLE VB.

TABLE VB

Initial statrting cone. 1800 ppm

After open cell pretreatment, no digestion 1130

After 1 hr undisturbe digestion 920

After 2 hrs undisturbed digestion 910

After cell stage 1 4 min 300

After 1 hr undisturbed digestion 120

After cell stage 2 1 min 0.59

The residue was a high grade metal hydroxide concentrate.

An important embodiment of this invention is based on our observation that when the ion state of the ions are undergoing modification in the cell (contiOlled oxidation) , the presence of a very strong magnetic field enhances and accelerates the process; The magnetic field is preferably a strong gradient field generated by the presence of the north magnetic pole. To illustrate this effect the following tests are presented.

EXAMPLE VI 650 ml of a well water sample was treated under identical conditions using a cell with and without a magnetic field. Each sample was treated for 2 min under identical conditions.in a cell having a type 3 stannite cell. The pH was measured before treatment, immediately after treatment and again 1 hr after passive digestion time. . The results are tabulated in TABLE VI

TABLE VI pH starting pH post treatment pH after 1 hr digestion

Test l No field 7.7 9.2 8.6

Test 2 9 south 7.7 9.6 7,5

Test 3 9 north 7.7 8.9 8.1

Test 4 13 south 7.7 9.8 8.6

Variations and modification of the apparatus and methods of the invenion may occur after reading the specification and studying the drawings which are within the scope of the invention.

For example, in some situations, it may be more feasible to use a different method for raising the pH other than adding the chemical solution of fig. 2. Such a method might be to bubble ammonia through the solution. In another situation, it may be feasible to raise the pH and apply the electro-hydrolysis process in a series of steps by adding the solution of fig. 2 in steps so as to remove at the lower pH the ion species that would interfere with removal of species at higher pH. As pointed out, Ca is one species that interferes with the removal of other species that precipitate only at higher pH.

INDUSTRIAL APPLICABILITY

This invention has wide application for removal of contaminating heavy and light metal ions from waste water and particularly for providing an efficient process for removing large concentrations of calcium and magnesium such as are found in desert waters in brines created from operations used in processing olives.

The invention is particularly useful for removing from water impurities such as selenium and arsenic (metallic and non metallic forms) which pose a hazard even when present in small concentrations.

In comparison with prior methods of treatment of spent processing solutions, the method and apparatus of the present invention is less complex in terms of required steps and additives required and consequently less costly.

Claims

What is claimed is:

1. A method for removing a group of species of metal ions from aqueous solution to be purified wherein at least one species of said group of metal ions has a multiple quantity of ionic states, each state characterized as having its own valence and solubility, said method including the steps in operable order in succession for each species:

(i) adjusting the pH of said aqueous solution to a value where there is sufficient available hydroxyl ions present to forrn hydroxides with all ions of each species when all ions of each species is in a highest valency state where said hydroxides are effectively insoluble;

(ii) passing said aqueous solution between at least one pair of electrodes with a potential between said at least one pah- of electrodes selected to convert said each species from a lower valency state to a highest valency state of said respective species whereby said each species forms with said hydroxyl ions a substantially insoluble hydroxide precipitate ;

(iii) holding said aqueous solution from step (ii) in a digesting tank for a period of time sufficient for insoluble precipitates of hydroxides of said respective ion species to form;

(iv) passing said solution from step (iii) through a means for removing said substantially insoluble precipitates from said aqueous solution.

2. The method of step 1 wherein said step (i) includes a step of adding to said aqueous solution an agent selected to raise said pH.

3 A method for removing a group of species of metal ions from aqueous solution to be purified wherein at least one species of said group of metal ions has a multiple quantity of ionic states, each state characterized as having its own valence and solubility, said method including the steps in operable order in succession for each species:

(a) adjusting the pH of said aqueous solution to a value between 7.5 and 9.5 by mixing into the aqueous solution a chemical agent formulated according to the following steps:

(i) adding 40 ml of concentrated sulfuric acid to each one liter of water;

(ii) adding Ca(OH)₂to bring the pH of said sulfuic acid up to a range 12.8 to 13.1;

(iii) passing the aqueous solution of step (ii) through a filter having a pore size no greater than eleven microns;

(iv) adding sufficient potassium hydroxide to bring the pH of said aqueous soluion of step (iii) to a range of 13.8 to 14.0 thereby producing a base solution; (v) adding magnesia in an amount of 10 grams per one liter of base solution.

(b) passing said aqueous solution between at least one pair of electrodes with a potential between said at least one pair of electrodes selected to convert said each species from a lower one of said ionic states to a highest valency state of said ionic states of said respective species whereby said each species forms a substantially insoluble hydroxide precipitate;

(c) holding said aqueous solution from step (b) in a digesting tank for a period of time sufficient for insoluble precipitates of hydroxides of said respective ion species to form;

(d) passing said solution from step (c) through a means for removing said substantially insoluble precipitates from said aqueous solution.

4. The method of claim 3 wherein step (b) includes the step of imposing a magnetic field between said electrodes while passing said aqueous solution between said electrodes.

5. The method of claim 3 wherein said group of species of metal ions includes calcium ions and step (b) performed immediately after initially adjusting the pH of said solution to a range between 7.5 and 9.5 includes the step:

passing said solution between tin electrodes of an ion state modification cell having a voltage between said electrodes in a range between 50.0 to 55.0 volts, whereby Ca(OH)3 precipitates are formed which are removed in step (d).

6. The method of claim 5 wherein said group of species of ions contains at least one of Cr, Cu, Zn, Mn, As, Se and SiO₂ ions and said steps following removal of Ca(OH)3 precipitates includes the steps:

selecting another pair of electrodes from a group of electrodes which consists of carbon, aluminum, iron and titanium;

imposing a voltage between said another pah- of electrodes having a value between said electrodes selected from a range of 79 to 83 volts;

passing said solution between said another pair of electrodes whereby said at least one of Cr, Cu, Zn, Mn, As and SiO ions form substantially insoluble hydroxide precipitates that are removed in step (d).

7. The method of claim 3 wherein said step (d) includes the step of selecting said means for removing to be at least one of a settling tank and a filter press.

8. An apparatus for performing the method of claim 3 wherein said group of ions has subgroups of species of ions wherein every species in any one subgroup require identical

conditions of pH, electrode material and voltage between electrodes for conversion to said highest valence state, said apparatus including a plurality of apparatus sections one section for each subgroup wherein each apparatus section comprises: a mixing container means for adding a selected agent to said aqueous solution to be purified to form a mixture such as to adjust a pH of said mixture to a required value;

a cell means containing a pair of electrodes selected for optimal conversion of the respective subgroup to said highest valency state;

said cell means communicating with said mixing container for converting an ionic state of said species of ions in said respective subgroup to said highest valency ;

a power supply means for applying a selected voltage between said selected electrodes wherein said selected voltage is in a range that is most efficient in converting said subgroup of ions from said lowest valency state to said highest valency state;

a digestion container means communicating with said cell means for holding said aqueous solution to be purified and permitting hydroxides of of every species in said respective subgroup to precipitate.

9. The apparatus of claim 8 which comprises means for applying a magnetic field between said electrodes.

10. The apparatus of claim 8 wherein said elecrodes are made from a material selected from a group of materials which consists of tin, carbon, titanium and aluminum.