Potassium cyanide (sodium) is colorless transparent crystal, often due to impurities and grayish yellow, easily soluble in water, solubility in water is greater than 20 rings, sexual toxicity. When its aqueous solution is acidified to pH 7, almost all of the cyanide is decomposed into volatile hydrocyanic acid gas. Hydrocyanic acid gas is a colorless and highly toxic gas. The hydrocyanic acid in solution is a weak acid, difficult to ionize, and has no leaching effect on gold and silver. When the pH value is 12, almost all of the cyanide in the solution dissociates into cyanide roots. Therefore, cyaniding must be carried out in an alkaline medium. It is generally believed that in the presence of oxygen, cyanide leaching of metal in the electrochemical corrosion process, The chemical equation for cyanide leaching of gold can be expressed as ZAu 14 4CN 1 02 ZHZO 1 ZAu(CN) tooth HZOZ 10 ZOH 1 ZAu 4CN 10 HZO: 1 ZAu(CN) spear ZOH- the synthesis is 4Au SCN 1 02 ZHZO 1 4Au(CN) tooth 10 4OH- The reaction of cyanide leaching of gold is mainly carried out in the direction of hydrogen peroxide formation with the participation of oxygen.
Cyanide gold leaching method
Methods Cyanide leaching of gold can be divided into two methods: percolating cyanide leaching and stirring cyanide leaching.
There are two kinds of percolation cyanide leaching method: tank leaching and pile leaching, and percolation tank leaching is often used to treat 3. mm gold bearing ore, coarser calcine. The ore is usually crushed below somm(or lomm) according to the natural gold distribution size and ore porosity. The smaller the ore block pull, the higher the gold leaching rate. The concentration of sodium cyanide in leaching is usually. .03%~. , 2%. The index of cyanidation depends on gold particle size, sulfide content, ore particle size, leaching rate, leaching time, cyanide concentration and washing degree of leaching residue. In the treatment of gold-bearing quartz sand, the leaching rate of gold can reach 85% to 90%. When the particle size is coarse, the leaching rate of gold decreases to 60%. The gold content in the noble liquid is low in the leaching process of leaching cyanide pile, so it is generally necessary to adsorb and enrich by activated carbon, and extract gold from the noble liquid obtained from the desorption of gold-loaded carbon by electrodeposition or zinc replacement. Stirring cyanide leaching method is often used for leaching particle size less than. The leaching of 3mm gold-bearing raw materials is carried out in a compressed air mixing tank, a mechanical mixing tank or a mixing tank. The leaching includes slurry solid-liquid separation, countercurrent washing, noble liquid zinc powder replacement and gold mud melting. The concentration of leached pulp is generally less than 3D%~33%, and when the slime content is high, the concentration of leached pulp should be less than 22%~ 25%. When the operation is added stone ash, so that the pulp pH 291 12; By filling air, the concentration of dissolved oxygen in the pulp can maintain the best ratio to the concentration of sodium cyanide. The concentration of sodium cyanide in pulp is usually. .02% one. .1%.
Most of the concentrators using the stirring cyanide process use the washing method to separate the noble liquid from the leaching residue. The washing method can be divided into three kinds: decanting method, filtration method and fluidized washing, and the most commonly used is continuous countercurrent decanting method (CCD method). The thickener used in this method can be divided into two kinds: single layer and multi-layer.
Many cyanide concentrators in China use 2~3 layers thickener for solid-liquid separation and continuous countercurrent washing to obtain noble liquid
In the air, potassium cyanide solution can slowly dissolve gold, this is the result of oxygen participation
So if it is fast to dissolve gold under sealed conditions, it is necessary to add some oxidant, such as hydrogen peroxide
2Au + 4KCN + H2O2 =2 + 2KOH
Add some acid; 4Au + 8CN- + 2H2O = 4[Au(CN)2]- + 4OH- can react off the resulting OH-; Accelerate the reaction;
Complex compounds are produced in potassium cyanide solution, which can be complexed with gold atoms.