Gold extraction by nitric acid pre-oxidation method - catalytic oxidation acid leaching method

1) Acid Pretreatment for catalytic oxidation of the arsenopyrite Chemical Metallurgy Institute, Chinese Academy of catalytic oxidation of the development of pretreatment arsenic leaching pyrite, the catalytic system is introduced into a dilute nitric acid and a surfactant structure of a multi polar group The composition - sodium lignosulfonate (NaL) composition. The method is carried out at 100 ° C and 400 kPa, and the arsenic-containing gold concentrate is subjected to catalytic oxidation acid leaching pretreatment, and the gold leaching rate is as high as 95% to 99%. The research focused on the reaction of FeAsS in this system.
Comparison of 1FeAsS in an aqueous solution of H 2 S0 4 -O 2 and HN0 3 -H 2 S0 4 -0 2 . Due to the low oxidation potential of FeAsS, there is a certain reaction rate even in the H 2 S0 4 aqueous system. After the addition of nitric acid, the reaction rate of the system increases. For example, at 100 ° C, 5 g / L of nitric acid is added, and the reaction reaches the same conversion rate, and the time is shortened to 1/2, and at 90 ° C, it is shortened by two times.
Due to the presence of HNO 3 , the behavior of FeAsS is different from that in the pure H 2 S0 4 system. In the latter, the rate is proportional to the first power of the oxygen partial pressure; and in the case of HNO 3 , the rate is independent of the oxygen partial pressure. Thus, the oxidation of FeAsS in an aqueous HNO 3 -H 2 S0 4 -O 2 system can be carried out at a lower operating pressure without requiring higher pressures as in sulfuric acid systems.
In the H 2 S0 4 system, the speed can be increased by increasing the acidity. When HN0 3 is present, the acidity is lowered and the reaction rate is greatly increased. Therefore, the leaching reaction of FeAsS in an aqueous solution of HN0 3 -HH 2 S0 4 -0 2 can be carried out at a lower acidity, so that the amount of H 2 S0 4 used can be saved.
Therefore, the oxidation of FeAsS in the HN0 3 -H 2 S0 4 -0 2 aqueous solution system is better than that in the H 2 S0 4 -0 2 aqueous solution; the main performance is to increase the reaction rate, reduce the reaction oxygen partial pressure and reduce The amount of acid consumed by the reaction.
2 Comparison of FeAsS and FeS 2 in HN0 3 -H 2 S0 4 -0 2 aqueous solution system. The activation energy value of FeS 2 is 38.5 kJ/mol, while the FeAsS is only 23.4 kJ/mol, which indicates that FeS 2 is harder to oxidize than FeAsS. The rate of FeS 2 is less affected by acidity and is different from FeAsS.
The relationship between the rate constant and the nitric acid concentration of FeS 2 and FeAsS in a HN0 3 -H 2 S0 4 -0 2 aqueous solution at 100 ° C is similar (1/K is linear with 1/c (HN0 3 )). However, the leaching rate of FeS 2 is more affected by the change of HN0 3 concentration than the leaching rate of FeAsS.
Although the gold concentrate containing FeS 2 and FeAsS is subjected to catalytic oxidation leaching pretreatment, it can be inferred that its operating conditions are mainly restricted by FeS 2 .
2) Recovery of silver from silver-containing sulfide concentrate by nitric acid-catalyzed oxygen pressure leaching . The Nitrox method, Arseno method and Redox method developed in the 1980s have been industrialized. When these methods are used to treat gold and silver stubborn ore, Gold and silver are recovered by subsequent cyanidation. Wu Peijin et al reported that only the nitric acid-catalyzed oxygen pressure leaching of silver-containing sulfide concentrate to recover silver and recycling of nitric acid.
Generally, when the raw material contains more than 7% sulfur, the high temperature method is adopted. For the silver concentrate which is more than 20% sulfur and belongs to the difficult pyrite type, the high temperature scheme is ideal, and the nitrogen oxide regeneration HN0 3 can be simplified. As for the recovery of Ag from the leachate, it is not suitable to use the Pb, Zn and Fe replacement method due to the strong acid medium. With the NaCl precipitation method, the residual chlorine has a corrosive effect on the stainless steel of the autoclave material, and is not feasible. Therefore, a method of depositing silver using thiocyanate is used.
Test primary metal ore minerals include pyrite 25%, 15% sphalerite, galena 6% Sulfate 6% to 7%, a sulfur-containing silver salt of 2% to 3%, 2% cassiterite, and Gangue stone. The chemical analysis results of the test are shown in Table 1.

Table 1 Test chemical analysis results
SiO 2
Al 2 O 3
Content w/%

Through the exploration and selection of leaching conditions, denitration conditions and immersion silver conditions, the final leaching system test results are shown in Table 2.

Table 2 leaching system test results
Shen Yin
Leaching silver
Regenerated nitric acid
Silver content / (mg·L -1 )
Silver recovery rate /%
NO 3 - content / (g · L -1)
Nitrogen oxide recovery rate /%
Denitrification leaching
Final leaching
Total silver leaching rate /%
Nitrogen oxide in exhaust gas
Recovery rate/%
Post-silver solution
Post-silver solution
Denitration liquid
Denitration slag containing silver / (g · L -1 )
Leach rate /%
Leaching residue containing silver / (g · L -1 )
Leach rate
Silver condition: KSCN dosage is 1.02 times stoichiometric, the concentration is 0.1994mol/L;
Denitration conditions: additional H + (H2SO4) concentration of 2.5mol / L, liquid-solid ratio of 5:1, stirring speed of 600r / min, total pressure of 800kPa, 110 ° C, residence time of 30min;
Leaching conditions: HNO 3 with a concentration of 2.5 mol/L, a liquid-solid ratio of 5:1, a stirring speed of 600 r/min, an oxygen partial pressure of 200 kPa, 130 ° C, and a residence time of 30 min.

It can be seen from Table 2 that the silver leaching rate is 97.69%, the nitrogen oxide cycle utilization rate is greater than 99.9%, and the exhaust gas contains NOx less than 100×10 -4 %, which meets the discharge standard.
In order to prevent the denitration process from entering lead iron and vanadium , an acid must be added. The high acid effluent produced by the external acid can be used for copper oxide or wet zinc smelting. Thus, the main consumption is oxygen, and the method is economical and reasonable.

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