WO2005108290A1

WO2005108290A1 - Improved process for production of pure amorphous silica from quartz preferably to be used as filler material

Info

Publication number: WO2005108290A1
Application number: PCT/NO2005/000154
Authority: WO
Inventors: Birger Langseth; Christian Rosenkilde; Natalia Loboda
Original assignee: Promeks ASA
Current assignee: Promeks ASA
Priority date: 2004-05-12
Filing date: 2005-05-12
Publication date: 2005-11-17
Anticipated expiration: 2006-11-12

Abstract

A process for production of amorphous silica from quartz includes the following steps: Heating (calcination steps) of quartz or another SiO2 based material with MgCl2 at a temperature of 800 - 1300 °C wherein the weight ratio of MgCl2 to quartz is greater than 2 and the presence of water vapour in excess of the stoichiometric amount needed to make MgSiO3 or Mg2SiO4; Leaching at temperatures preferable between 50 and 150 °C of the produced silicate with HCl to form a solution of MgCl2 with insoluble silica; Separation of insoluble silica from the solution; Recycling of MgCl2 to the heating step and the HCl solution to the leaching step. Other chlorines such as BeCl2, CaCl2, SrCl2 and BaCl2 may be used in the process instead of MgCl2.

Description

IMPROVED PROCESS FOR PRODUCTION OF PURE AMORPHOUS SILICA FROM QUARTZ PREFERABLY TO BE USED AS FILLER MATERIAL

The present invention relates to the production of pure amorphous silica from quartz or other SiO₂ based raw materials. Several types of silica can be produced by using the techniques described in this application. Common for most of them is the purity of the silica, which is higher than commercial silicas on the marked today. The silica content in the product silica might be as high as 99.98%. The various types of silica can be used for beer stabilization, insulation, catalysts and silicon rubber, and other applications that require pure silica. There are small differences during the production process for the various types of silica.

Amorphous silica is mainly produced by acidulation of a soluble silicate, commonly by addition of sulphuric or hydrochloric acid to a sodium silicate (water glass) solution. The products are either precipitated silica or silica gel depending upon details in the production process. Also other known processes (silicon tetrachloride/alkoxide reacts with hydrogen and oxygen to form fumed silica) are used commonly in the present silica industry.

Methods for preparation of amorphous silica from soluble silicates is well established, but suffer from the disadvantage that soluble alkali silicate and mineral acid are consumed in the production process. Furthermore, these silica products often contain rather high amounts of alkali metals, which is unwanted for many applications.

US patent No. 1 ,868,499 relates to a process for recovering alumina from silicious materials where silica is considered as an unwanted by-product and no further processing of this product is carried out.

Further, US patent No. 4689315 describes a method for the production of amorphous silica particles where the lime and the hydrochloric acid are consumed in the process. European patent, EP 1265812 B1 , relates to a process for the preparation amorphous silica where the raw materials are similar to the present invention, but where the process is limited with respect to the type of silica that can be produced, the purity of the silica product and that CaCI₂ is the only reagent used in the mixture with the raw materials.

Common for all prior art solutions is that no provisions are made with regard to the possibilities for the silica product, no description of the silica product is given and nothing is stated about the applications for the various types of pure silica products.

The silica product according to the present invention is very pure, having an amorphous silica content of more than 90%, and it can be used for several applications that never have been investigated before. The chemical impurities are at a much lower level than the commercial silica types, and the produced amorphous silica can have a very high surface area. The silica is produced from quartz or other SiO₂ based materials and all other reagents, chemicals like mineral acid and chlorides from all elements in the group II of the periodic table (Be-Mg-Ca-Sr-Ba-Ra), used in the process are recycled. Only minor amounts for make-up of these chemicals are required.

The invention according to the present invention will be further described in the following with reference to the attached drawing showing, by means of a flow diagram, the main steps of the process.

The process according to the invention for production of amorphous silica from quartz include the following steps:

Step 1.

Heating the crushed (< 100 μm) quartz together with MgCI₂ or CaCI₂ or other chlorides like BeCI₂, SrCl₂ and BaCI₂, in the following referred to as MeCI₂ , to a temperature in the range 800 - 1300 ^c preferably over a two stage calcinations step for a period of 0.5 to 3 hours, depending on the temperature, wherein the ratio of MeCI₂ to the quartz is greater than 2 and in the presence of water vapour in excess of the stoichiometric amount (preferable at least 7%) needed for the reaction: x MeCI₂ + y SiO₂ + x H₂O - (MeO)x * (SiO₂)y + 2x HCl wherein x is greater than y in order to obtain a conversion of quartz to magnesium (or calcium) silicates in excess of 99.9%. The HCl produced during calcination is absorbed in a scrubber and via step 4 reused in step 2.

Step 2.

Leaching of the metal silicate with HCl, preferably an excess of HCl of at least 20%, to form a solution of MeCI₂ with insoluble silica by addition of the HCl solution to a reactor containing the silicate either in the form of powder or as a water slurry

Step 3.

Separating insoluble silica from the solution using filters (belt filter, press filter, filter press etc.) or another separation method. The solution contains excess of HCl, MeCI₂ and impurities.

Step 4.

Recycling of the chloride solution to step 1 and the HCl solution to step 2 using a recovery system in order to separate the solutions. The impurities are removed prior to the reuse of the solutions in order to avoid build-up of impurities. Several techniques can be used to remove impurities depending on the amount impurities in the raw materials, but one way is to precipitate impurities as hydroxides at elevated pH. Silica of types C and D are alkaline-set silica gels. Leaching is made by addition of acid to bake powder or to bake slurry, which is preferable.

Example 1.

Silica C (filler in rubber).

Leaching. 1000 litres of 20% HCl was fed to the reactor filled with 200kg of calcium silicate produced according to step 1. Acid feeding took about 45 minutes under agitation. The reactor was heated to 100°C, the agitator was operateed with 100% speed. The leaching proceeded at this temperature for 90 minutes. After cooling of the leaching slurry to 40°C-45°C the reactor was emptied to an intermediate tank from which the leaching slurry was passed to a filter press. Filtration and washing.

Filtration and washing were made at the filter press under squeezing. After the first filtration and washing the silica was repulped and again filtered and washed. The washing procedure was controlled by the chloride content in the wash water and in wet cake (<50ppm).

Drying. The wet cake was dried in a Barr-Rosin ring drier. The silica properties were as follows.

Surface Pore Pore Bulk Oil Purity, pH area, volume, radius, density, absorption, %SiO2 (5%) m2/g ml/g nm g/ml ml oil/1 OOg

310-350 0.28-0.34 4.0-4.2 0.28-0.30 130-140 99.8 4.3

Particle size (D₅₀) of silica C is 20-30micron

Example 2.

Silica D (filler in rubber).

Leaching.

1400 litres of 20% HCl was fed to a reactor filled with 200kg of calcium silicate produced according to step 1. The reactor was heated to 150°C, the agitator was operated with 100% speed. The leaching proceeded at this temperature for 180 minutes. After cooling of the leaching slurry to 40°C -45°C the reactor was emptied to an intermediate tank from which the leaching slurry was passed to a filter press. Filtration and washing.

Filtration and washing were made at the filter press under squeezing. After the first filtration and washing the silica was repulped and again filtered and washed. The repulping and washing procedures should be repeated at least twice to get pure silica. The washing procedure was controlled by the chloride content in the wash water and in wet cake (<50ppm). Drying. The wet cake was dried in a Barr-Rosin ring drier. The silica properties are as follows.

D₅₀ is 25-35 micron.

Claims

Process for production of amorphous silica from quartz characterised by the following steps:

• heating (calcinations step) of quartz with MgCI₂ , CaCI or other metal chlorides (in the following denoted MeCI₂) at a temperature of 800 - 1300 °C wherein the weight ratio of MeCI₂ to quartz is greater than 2 and the presence of water vapour in excess of the stoichiometric amount needed

• leaching at temperatures preferable between 50 and 130 °C of the produced calcium silicate with HCl to form a solution of MeCI₂ with insoluble silica, whereby the leaching is preferably made by addition of acid to bake powder or to bake slurry

• separation of insoluble silica from the solution

• recycling of MeCI₂ to the heating step and the HCl solution to the leaching step

Process in accordance with claims 1 , characterised in that the calcination step is carried out in two steps where the temperature for the first step is kept below 1000 °C and for the second step the temperature might be as high as 1300 °C

Process in accordance with claims 1 -and 2, characterised in that metal impurities such as Fe, Al and Ti are removed prior to reuse of the chlorine and acid solutions

Process in accordance with claims 1-3 characterised in that after the first filtration and washing the silica is repulped and again filtered and washed, whereby the washing procedure is controlled by the chloride content in the wash water and in wet cake (<50ppm).