Removing cyanide from effluents

ANNOUNCEMENT

[B] (11) EXPLANATORY WRITING 7 4 6 9 3 ^{c (45)} ,,. 3 - H - o (51) Kv.lk.⁴/lnt.CI.⁴ C 02 F 1/58, 1/70, 1/72

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<td> (21)</td><td>Patent application - Patent application</td><td> 833649</td>

<td> (22)</td><td>Application date - Application date</td><td> 07.10.83</td>

<td> (23)</td><td>Start date - Validity day</td><td> 07.10.83</td>

<td> (41)</td><td>Became public - Became public</td><td> 14.04.84</td>

<td> (44)</td><td>Date of display and publication. Application submitted and the publication published</td><td> 30.11.87</td>

<td> (86)</td><td>Kv. application - Int. application</td><td></td>

(32) (33) (31) Privilege requested-Requested priority 13.10.82

Republic of South Africa-South African Republic (ZA) 82/7482 Implemented-Styrkt (71) Johannesburg Consolidated Investment Company Limited, 66 Acacia Road, Primrose East, Germiston, Transvaal, South Africa South Africa (ZA) (72) Colin Walter Alexander Muir, Sandton, Transvaal, FIELD OF THE INVENTION to reduce the concentration and cyanide ion content.

(57) SUMMARY

For example, this method is used for the treatment of the cyanide process by contacting the powder with the powder and the reduction of the base metal cyanide and the cyanide process.

Method for treating cyanide - containing effluents

The invention relates to a method for treating effluent containing metal cyanide complexes and free cyanide to reduce the metal and cyanide content of the effluent.

Wastewater from some industrial processes contains cyanide in high concentrations either as a free ion or as a complex with base metals. Before being discharged into the environment, such effluent requires a treatment that removes cyanide and many of the base metals.

Known processing methods use relatively expensive reagents and may also form toxic cyano compounds.

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

In the process of the invention, the effluent is contacted with at least about 5 g of powdered sulfur and at least about 11.5 g of metallic iron per 500 ml of effluent at a pH of at least 8 and a temperature between 50 ° and the boiling point of the effluent. after which the effluent is filtered.

U.S. Patent No. 2,194,438 describes a process for treating cyanide-containing waste solutions in which the waste solution is contacted with elemental sulfur and water-soluble polysulfide compounds under basic conditions. Sodium hydroxide is used as the basic substance. This method does not use iron or another metal of the same type as the method of the present invention. The method according to the invention is more advantageous from the point of view of occupational safety than the method according to the publication of the said US patent, because the use of sodium hydroxide is avoided.

U.S. Patent No. 4,250,030 also discloses a process for removing free or complex cyanide from wastewater. However, this process differs from the process of the invention in that the cyanide removal is performed using insoluble solid ferrous sulfide. In addition, a reducing agent such as ferrous ions or sodium sulfite may be used in the process of that U.S. patent.

In the practical application of the method according to the invention, sulfur and iron veneer flour were mixed with the effluent, but other forms of mixing are also assumed to be effective.

So far, the optimal additions of sulfur and elemental iron have not been determined, but when there was less than half the amount of iron, good results were obtained.

Various effluents containing base metal complexes and free cyanide as well as antimony arsenic complexes were mixed with powdered sulfur and ferrous flour together with a filtration aid. Five grams of sulfur, 11.5 g of iron flour and 5 g of filtration aid were used for each 500 ml of effluent. The effluent was stirred for 4 hours in Experiment 1 and 24 hours in the other experiments at 80 ° C and a pH of 8.

The slurry was filtered and the following results were obtained:

Test 1

<td rowspan="3">Analytical sample of the original solution Analysis sample of the filtrate</td><td>Cu mg / £</td><td>Ni mg / £</td><td>'F e mg / £</td><td>Co mg / £</td><td>As mg / £</td><td>Sb mg / £</td><td>CN- 1 mg / £ </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>ES '</td>

<td> 0,04</td><td> 3,6</td><td> 1,8</td><td> 0,91</td><td> 0,92</td><td> 0,41 ¹</td><td> &lt;0,1 :</td>

ES = not available

Test 2

<td></td><td>Cu mg / £</td><td>My mg / £</td><td>Fe mg / £</td><td>Sb mg / £</td><td>As mg / £</td>

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

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

Test 3

<td> -</td><td>Cu mg / Z</td><td>Ni mg / £</td><td>Co mg / £</td><td>Fe mg / £</td><td>As mg / £</td><td>Sb mg / £</td><td>CKmg / £</td>

<td>Originally</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 according to the invention provides a process for reducing the content of base metals to a very considerable extent which occurs after cyanidation.

Test 4

In a large-scale operation, it is practical to use scrap iron rather than iron powder. In this case, it is necessary to ensure that the surfaces are clean and not oxidized, and after degreasing, washing with dilute hydrochloric acid is necessary. It is also necessary to make the iron active by conditioning with other ingredients, namely finely divided sulfur and effluent solution at the required temperature.

As soon as the surface of the scrap iron is conditioned, reagents comprising unreacted scrap, sulfur and diatomaceous earth, together with the precipitate formed, can be used to initiate the reaction in subsequent stages of effluent treatment, as shown in the data in the following tables.

<td></td><td>Au mg / C</td><td>Cu mg / €</td><td>Ni mg / £</td><td>Fe mg / £</td><td>As mg / £</td><td>Sb mg / €</td><td>CNmg / £</td>

<td>Analytical sample of the original solution</td><td> 23,7</td><td> 124</td><td> 121</td><td> 195</td><td> 4,0</td><td> 1 1 11 ,4</td><td> 458</td>

After treating a 500 ml sample for 24 hours at 80 ° C with 20 g of purified iron chips and 5 g of powdered S using 1 g of diatomaceous earth as a collector, the following results were obtained:

<td></td><td>Au mg / £</td><td>Cu mg / £</td><td>Ni mg / €</td><td>Fe mg / £</td><td>As mg / £</td><td>Sb mg / £</td><td>free CNmg / i</td>

<td>Analytical sample of the solution</td><td> 0,01</td><td> 0,06</td><td> 5,6</td><td> 0,33</td><td> —</td><td> 0,3</td><td> 33</td>

After an additional 500 ml was treated with recycled solids from the previous experiment for 24 hours at 80 °

In C, the analytical sample of the solution was as follows:

<td></td><td>Au mg / f</td><td>Cu mg / €</td><td>Ni mg / €</td><td>Fe mg / £</td><td>As mg / f</td><td>Sb mg / ^</td><td>free CNmg / €</td>

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

The recycled solids were then re-used to treat a 500 ml sample, which was a more concentrated effluent with the following analytical sample:

<td></td><td>Au mg / €</td><td>Cu mg / €</td><td>Ni mg / f</td><td>Fe mg / €</td><td>As mg / £</td><td>Sb mg / €</td><td>CN ' mg / f</td>

<td>effluent analysis sample</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>

after 1 hour at 80 ° C the result was as follows:

<td></td><td>Au mg / €</td><td>Cu mg / f</td><td>Ni mg / €</td><td>Fe mg / f</td><td>As mg / €</td><td>Sb mg / £</td><td>CN 'mg / f</td>

<td>treated effluent</td><td> 3,8</td><td> 0,27</td><td> 7,7</td><td> 5,53</td><td> —</td><td> 0,32</td><td> 37,5</td>

Test 5

The series was repeated in Experiment 5 using iron file flour collected from a workshop grinding wheel. The material, which apparently contained some corundum, was purified in the same manner as in Experiment 4. The same effluents were used, with the same operating parameters. The results are given in the following tables:

Analytical sample of the original effluent as in experiment 4.

<td></td><td>Au mg / €</td><td>Cu mg / f</td><td>Ni mg / f</td><td>Fe mg / €</td><td>As mg / C</td><td>Sb mg / €</td><td>CN mg / €</td>

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

<td>t 1 Analytical sample after □ solids recycling _________</td><td> 0,01</td><td> 0,02</td><td> 0,3</td><td> 1,48</td><td> —</td><td>ES</td><td> 38</td>

ES = not available

Analytical sample of concentrated effluent - as in experiment 4.

<td></td><td>Au mg / i</td><td>Cu mg / £</td><td>Ni mg / €</td><td>Fe mg / €</td><td>As mg / €</td><td>Sb mg / f</td><td>CN mg / e</td>

<td>Analytical sample after the second round of solidification</td><td> 3,59</td><td> 0,3</td><td> 1,0</td><td> 0,2</td><td> -</td><td> 0,3</td><td> 32</td>

These results indicate that it is possible to treat the concentrated cyanide-containing effluent in one or more tanks equipped with a stirrer continuously. An efficient heat exchange system uses the solution leaving the system to heat the incoming effluent.

It is also believed that a denser scrap iron could be used after suitable conditioning, thus ensuring that the requirements of the method for reagents would be economically advantageous.