Removing cyanide from effluents

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Application number International filing date Filing date for European patent application Priority information

82-10-13 ZA 82/7482

87-02-23

84-04-14

83-10-06

83-10-06 (30) (11)

Publication number 44g 44g

Application received as:

H Swedish patent application

O completed international patent application with number □ converted European patent application with number (71) Applicant Johannesburg Consolidated Investment Co Ltd, Germiston ZA (72) Inventor CW A. Muir, Sandton (74) Agent AWAPATENT AB (54) Designation Procedure for processing an emission containing metal cyanide complexes and free cyanide (56) Published publications: US A 2 194 438, US A 3 931 007, US A 4 250 030 (57) Abstract:

Emissions from cyanidization operations are treated by contacting the emission with powdered sulfur and iron to reduce the base metal content and cyanide ion content in the emissions.

DB 603415 i

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Background of the invention

The present invention relates to the treatment of cyanide-containing emissions.

Waste emissions from certain industrial processes contain high levels of cyanide either as free ions or complexed with base metals. Before such an emission is released into the environment, this requires treatment to remove the cyanide and many of the base metals from the solution.

Known treatment processes use relatively expensive reagents and can also produce toxic cyanogen compounds.

The present invention is based on an unexpected result obtained by the inventors.

Summary of the Invention

According to the invention, an emission containing metal cyanide complexes and free cyanide is treated to reduce the metal and cyanide content therein by contacting the emission with powdered sulfur and metallic iron, for example in the form of iron filings, whereby the amount of sulfur is less than half the amount of iron. a temperature of between 50 ° C and the boiling point of the emission, after which the emission is filtered.

In practical application, the sulfur and the iron file chips are stirred in the discharge, but it is believed that other forms of mixing are also effective.

The optimum additions of sulfur and elemental iron have not yet been determined, but when the sulfur was less than half the mass of the iron, good results were obtained. Example

Various discharges containing base metal complexes and free cyanide as well as antimony and arsenic complexes were stirred with powdered sulfur and iron filings along with a filter aid. 5 g of sulfur, 11.5 g of iron file chips and 5 g of filter aid were used for each 500 ml of

448 449 the emission. The discharge was stirred for 4 h in the case of experiments and 24 h in the case of the other experiments at a temperature of 80 ° U and a final pH of 8.

The slurry was filtered and the following results were obtained:

Test 1

<td></td><td>Cu mg / l</td><td>Ni mg / l</td><td>Fe mg / l</td><td>Co mg / l</td><td>If mg / 1</td><td>Sb mg / l</td><td>CNMG / 1</td>

<td>Analysis of the original solution</td><td> 28,9</td><td> 48,1</td><td> 1,5</td><td> 3,15</td><td> 7,9</td><td> 153</td><td>NA</td>

<td>Analysis of the filtrate</td><td> 0,04</td><td> 3,6</td><td> 1,8</td><td> 0,91</td><td> 0,92</td><td> 0,41</td><td> &lt;0,1</td>

NA, = not available

Test 2

<td></td><td>Cu mg / l ...</td><td>Ni mg /¹</td><td>Fe mg / l</td><td>Sb mg / l</td><td>As ^m?/in</td><td colspan="2"></td>

<td>Analysis of the original solution</td><td> 183</td><td> 326</td><td> 75</td><td> 36,1</td><td> 77,3</td><td></td><td></td>

<td>Analysis of the filtrate</td><td> 0,28</td><td> 1,1</td><td> 85</td><td> &lt;0,1</td><td> &lt;1</td><td></td><td></td>

<td>Test 3</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td></td><td>Cu mg / l</td><td>Nine mg / i</td><td>Co mg / l</td><td>Fe mg / l</td><td>If mg / 1</td><td>Sb mg / l</td><td>CNMG / 1</td>

<td>Original solution</td><td> 1200</td><td> 209</td><td> 293</td><td> 50</td><td> 12,8</td><td> 130</td><td> 1031</td>

<td>Filtrate</td><td> 0,52</td><td> 1,1</td><td> 1,4</td><td> 66</td><td> &lt;1</td><td> &lt;1</td><td> 59</td>

The results show that the process of the invention provides a way to greatly reduce the concentration of base metals found after cyanidization.

Test 4

On a large scale, it is practical to use iron scrap rather than iron powder. It is then necessary to ensure that the surfaces are clean and not oxidized and, after degreasing, a wash with dilute hydrochloric acid

448 449 necessary. It is also essential that the iron is made active by conditioning with the other constituents, namely, finely powdered sulfur and the emission solution at the required temperature.

Once the surface of the iron scrap has been conditioned, the reagents, including unreacted iron scrap, sulfur and diatomaceous earth, together with the precipitate formed, can initiate a reaction in further sequences of emission treatment, as the data in the tables below show.

<td></td><td>Au mg / l</td><td>Cu mg / l</td><td>Ni mg / l</td><td>Fairy mg / 1</td><td>If mg / 1</td><td>Sb mg / l</td><td>CNMG / 1</td>

<td>Analysis of original solution</td><td> 23,7</td><td> 124</td><td> 121</td><td> 195</td><td> 4,0</td><td> 11,4</td><td> 458</td>

After treatment of 500 ml with 20 g of purified iron filings and 5 g of powdered S with 1 g of diatomaceous earth as a collector for 24 hours at 80 ° C:

<td></td><td>Au mg / l</td><td>Cu mg / l</td><td>Ni mg / l</td><td>Fairy mg / 1</td><td>If mg / 1</td><td>Sb mg / l</td><td>Free CNmg / 1</td>

<td>Analysis of the solution</td><td> 0,01</td><td> 0,06</td><td> 5/6</td><td> 0,33</td><td>zero</td><td> 0,3</td><td> 33</td>

After treating an additional 500 ml with the recycled solids from the previous test for 24 hours at 80 ° C, the solution analysis was as follows:

<td></td><td>Au mg / l</td><td>Cu mg / l</td><td>You . mg / 1</td><td>Fe mg / i</td><td>As mg / 1</td><td>Sb .mg / 1</td><td>Free CNmg / 1</td>

<td></td><td> 0,01-</td><td> 0,95</td><td> 0,5</td><td> 0,15</td><td>zero</td><td> 3,1</td><td> 50</td>

The recycled solids were then used again to treat 500 ml of a more concentrated discharge with the following analysis;

<td></td><td>Au mg / l</td><td>Cu mg / l</td><td>Ni mg / l</td><td>Fe mg / l</td><td>If mg / 1</td><td>Sb mg / l</td><td>CN * mg / l</td>

<td>emissions Analysis</td><td> 16,6</td><td> 286</td><td> 110</td><td> 17,7</td><td> 9,9</td><td> 25,7</td><td> 2352</td>

448 449 with the following results after 24 hours at 80 ° C:

<td></td><td>Au mg / 1</td><td>Cu mg / l</td><td>Ni mg / l</td><td>Fairy mg / 1</td><td>As mg / 1</td><td>Sb mg / l</td><td>C1 mg / l</td>

<td>Treated emissions</td><td> 3,8</td><td> 0,27</td><td> 7,7</td><td> 5,53</td><td>zero</td><td> 0,32</td><td> 37,5</td>

Test 5

The sequence was repeated in test 5 using iron file chips collected from a mill wheel in a workshop. The material that apparently contained a certain proportion of corundum was purified in the same way as in test 4. The same emission was used, with the same operating parameters. The results are given below.

Analysis of original emissions as in test 4.

<td></td><td>Au mg / 1</td><td>Cu mg / in</td><td>You mg / 1</td><td>Fairy mg / 1</td><td>As mg / 1</td><td>Sb mg / l</td><td>CN . mg / 1</td>

<td>Analysis of treated solution</td><td> 0,01</td><td> 0,06</td><td> 0,9</td><td> 0,18</td><td>zero</td><td> 1,0</td><td> 32</td>

<td>Analysis after solids recirculation</td><td> 0,01</td><td> 0,02</td><td> 0,3</td><td> 1,48</td><td>zero</td><td>NA</td><td> 38</td>

NA = not available

Analysis of original emissions as in test 4,

<td></td><td>Au mg / l</td><td>Cu mg / l</td><td>Ni mg / l</td><td>Fairy mg / 1</td><td>If mg / 1.</td><td>Sb mg / l</td><td>CN m? /¹</td>

<td>Analysis after the second cycle of solids</td><td> 3,59</td><td> 0,3</td><td> 1,0</td><td> 0,2</td><td>zero</td><td> 0,3</td><td> 32</td>

These results show that it is possible to treat concentrated cyanide emissions in one or more stirred tanks in a continuous manner. Assuming an efficient heat exchanger system, the solution leaving the system can be used to heat incoming emissions.

It is also believed that denser iron scrap can be used after appropriate conditioning, thus ensuring that the reagent needs for the process are cheap.

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