GB2111035A - Treatment of sand - Google Patents

Abstract

A process for treating sand includes one or more stages in which the sand is subjected to mechanical attrition in the presence of zinc or sodium hydrosulphite and an acid selected from sulphuric acid and hydrofluoric acid at a solids content of at least 70% by weight and preferably at least 80% by weight. The process improves the overall efficiency of sand purification and may be used to purify sand to the high grade silica sand specification required for the preparation of colourless glass.

Description

SPECIFICATION Treatment of sand This invention relates to the treatment of sand.

Many techniques exist for the production of high quality silica sand and beneficiation methods are normally related to the level of contaminant in the raw material. Generally the industrial processing routes follow a basic pattern and include the washing of sand by a variety of techniques. Essentially the washing of sand is undertaken using simple settling cones, upward current washing or screw classifiers. Each of these techniques is normally employed to remove the finer fraction material and relies largely on differential settling based mainly on size distribution of monomineralic material. Further, as the product will be granular in a size range exceed 75 lim settling will also remove the materials of low specific gravity such as clays and organic materials.

Numerous methods for the further treatment of sand have also been conducted using chemical and mechanical means. Chemical means include the retention of sand in a reactor drum at a temperature of between 110 to 120"C 20% w/w HCI or alternatively the treatment of sand in a highly acid medium (controlled by hydrofluoric acid), and the addition of zinc hydrosulphite (Hydros). In both techniques the iron oxide is taken into solution and removed from the grain surfaces. The mechanical means of purifying sand largely depends on attrition scrubbing whereby grain to grain abrasion takes place, causing the sand grain surfaces to be cleaned by reducing clay and iron minerals.

Virtually all sand deposits require some form of beneficiation to reduce the Fe203 content to a level suitable for use in the preparation of colourless glass. Generally this level is about 0.03% Fe2O3.

It is an object of the present invention to provide a process for treating sand which can be used to reduce the Fe2Os content to a level suitable for use in the preparation of colourless glass.

According to the invention there is provided a process for treating sand which includes one or more stages in which the sand is subjected to mechanical attrition in the presence of zinc or sodium hydrosulphite and an acid selected from sulphuric acid and hydrofluoric acid at a solids content of at least 70% by weight and preferably at least 80% by weight.

It has been found that by attrition scrubbing of the sand grains in the presence of zinc or sodium hydrofluoric acid and sulphuric acid a quick and effective method of removing iron impurities from the sand is provided. The treatment stage may vary in time generally from 1 to 20 minutes and it has been found that the effect generally takes place during the first five minutes of treatment. The treatment stage is referred to herein as an "attreatment" stage. On completion of the attreatment stage, the sand is washed eliminating iron in solution and the attreatment stage may be repeated several times to increase the purity of the product.

Whilst the attreatment stage is particularly effective in eliminating the surface iron coatings, it also has the effect of improving the cleanliness of all grain surfaces to the same extent, largely by producing a more active surface.

Prior to the attreatment stage the sand which has been quarried is passed to a processing plant where it is washed and screened to a suitable particle size. If desired, the sand may be subjected to any of the known chemical or mechanical cleaning techniques prior to the attreatment stage.

The invention will now be illustrated by the following Examples.

Example 1 (prior art) A sample of silica sand was washed and subjected to mechanical attrition in an attrition scrubbing machine in the following stages: a) Washing 1) washed through No. 25 sieve 2) sand slurry washed into Denver at 10% pulp density 3) agitated at 1700 rpm for 21/2 minutes 4) water decanted off after 30 seconds settling time 5) No. 4 repeated four times 6) sand filtered and sampled.

b) Attrition 1) sand slurry at 70% pulp density in attrition cell 2) agitated at 1700 rpm for 10 minutes 3) washed into Denver Float Cell and washed until liquor was clear 4) filtered and sampled.

The iron oxide content of the silica sand at the various stages was as follows: iron oxide % by weight original sample 0.35 sample washed 0.19 sample washed and mechanically attrited 0.069 sample washed, mechanically attrited and floated 0.062 Example2 (prior art) A sample of silica sand was subjected to washing followed by cold leaching with zinc hydrosulphite and a hydrofluoric acid and thereafter subjected to a further washing and flotation in the following stages: a) Washing 1) washed through No. 25 sieve 2) sand slurry washed into Denver at 10% pulp density 3) agitated at 1700 rpm for 21/2 minutes 4) water decanted off after 30 seconds settling time 5) No. 4 repeated four times 6) sand filtered and sampled.

b) Treatment 1) sand slurry at 60% placed in beaker 2) slurry agitated, with paddle 3) 1.6 kgte-l hydrofluoric acid and 0.5 kgte- zinc hydrosulphite added 4) slurry agitated for 5 minutes 5) sand repeatedly washed until pH = 7.0.

c) Flotation 1) conditioned at 60% pulp density 2) pH to 2.25 with sulphuric acid, 500 gte- petroleum sulphonate 3) conditioned at 1700 rpm for 5 minutes 4) floated at 30% pulp density for 5 minutes 5) 400 gte-1 Comprox added at start of float.

The iron oxide content of the silica sand at the various stages was as follows: iron oxide % by weight original sample 0.35 sample washed 0.19 sample washed and treated 0.13 sample washed, treated and floated 0.057 Example 3 (in accordance with the invention) A sample of silica sand was washed and thereafter subjected to an attreatment stage in accordance with the invention. In the attreatment stage the sand was subjected to mechanical attrition in an attrition scrubbing machine in the presence of zinc hydrosulphite and a hydrofluoric acid at 80% by weight solids for five minutes. After attreatment the sample was subjected to washing and flotation and the attreatment/ washing cycle repeated three times.The steps of the various treatments were as follows: a) Washing 1) washed through No. 25 sieve 2) sand slurry washed into Denver at 10% pulp density 3) agitated at 1700 rpm for 21/2 minutes 4) water decanted off after 30 seconds settling time 5) No. 4 repeated four times 6) sand filtered and sampled.

b) Attreatment 1) sand slurried at 80% solids in attrition cell 2) 500 gte- Hydros and 1.0 kgte-' sulphuric acid added 3) slurry agitated for 10 minutes at 1700 rpm 4) sand repeatedly washed until washer liquor pH 7.0.

c) Flotation 1) conditioned at 60% pulp density 2) pH to 2.25 with sulphuric acid, 500 gte-' petroleum sulphonate 3) conditioned at 1700 rpm for 5 minutes 4) floated at 30% pulp density for 5 minutes 5) 400 gte- Comprox added at start of float.

The iron oxide content of the silica sand at the various stages was as follows: iron oxide % by weight original sample 0.35 sample washed 0.19 sample washed and attreated 0.056 sample washed, attreated and floated 0.048 sample washed, attreated three times and floated 0.030 The following Table compares the data from Examples 1 to 3.

TABLE attrition chemical attreatment Iron oxide content (Example 1) treatment (Example 3) (Example 2) original sample 0.35 0.35 0.35 sample washed 0.19 0.19 0.19 + treatment 0.069 0.13 0.056 + flotation 0.062 0.057 0.048 3 x treatment - 0.030 It will be seen that the attreatment stage in accordance with the invention improves the overall efficiency ofthe sand purification.

The process of the invention may be used to purify sand to the high grade silica sand specification required for the preparation of colourless glass.

Claims (12)

CLAIMS (Filed on 25/10/82)

1. A process for treating sand which includes one or more attreatment stages in which the sand is subjected to mechanical attrition in the presence of zinc or sodium hydrosulphite and an acid selected from sulphuric acid and hydrofluoric acid at a solids content of at least 70% by weight.

2. A process as claimed in Claim 1, in which the attreatment is conducted at a solids content of at least 80% by weight.

3. A process as claimed in Claim 1 or Claim 2, in which the sand is subjected to mechanical attrition in the presence of zinc hydrosulphite and sulphuric acid.

4. A process as claimed in Claim 1 or Claim 2, in which the sand is subjected to mechanical attrition in the presence of zinc hydrosulphite and hydrofluoric acid.

5. A process as claimed in any preceding claim, in which the attreatment is conducted in a mechanical attrition scrubber.

6. A process as claimed in any preceding claim, in which the sand is subjected to the attreatment for a period of from 1 to 20 minutes.

7. A process as claimed in any preceding claim, in which the sand is washed after the attreatment.

8. A process as claimed in any preceding claim, in which the sand is subjected to a plurality of attreatment stages.

9. A process as claimed in Claim 8, in which the sand is subjected to 3 attreatment stages with washing between each stage.

10. A process as claimed in any preceding claim, in which the sand is subjected to washing and screening prior to attreatment.

11. A process as claimed in any preceding claim, in which the sand is subjected to flotation after attreatment.

12. A process as claimed in Claim 1 substantially as herein described with reference to Example 3.