The ore heap should be washed with water and alkali before spraying the cyanide solution, and the cyanide solution should be sprayed when the pH value of the washing solution reaches 9.5-11.
1) Spray equipment
Uniform liquid distribution is one of the important factors to increase the leaching rate. There are two ways of liquid distribution: spraying liquid and dripping liquid. Regardless of the liquid distribution method, the leachate should cover the entire ore heap. The flow at each point on the surface is balanced, and the evaporation and drift are small. The liquid distribution system should use corrosion-resistant materials, such as polyvinyl chloride plastic.
① Ore washing
In order to reduce the consumption of cyanide and alkali, before spraying the cyanide solution in the ore heap, carry out alkali washing (washing with water first and then alkali washing if necessary), and CaO aqueous solution or NaOH aqueous solution can be used. Lime aqueous solution is cheap, but it takes a long time to wash ore and is prone to calcium formation, while NaOH aqueous solution has a short washing time and is expensive. When the pH value of the solution flowing out of the ore pile reaches 9.5-11 (generally 3-5 days), NaCN can be used Spray leaching with a mixture of alkali and alkali.
② Spray leaching
During heap leaching, the concentration of cyanide, alkali, and oxygen must be maintained appropriately.
Sodium cyanide concentration, the concentration of sodium cyanide in the leaching solution is generally controlled between 0.02 and 0.1%.
The concentration of NaCN should be controlled in stages, generally 0.08-0.1 at the beginning, 0.05-0.06% in the middle period, and 0.02-0.05% in the later period. Measure the cyanide concentration and pH value of the leachate regularly during production, and adjust them as needed, usually once or twice a day.
③ Spray intensity
The spray intensity is generally 10-20 liters/m2.
The size of the ore heap is large and the permeability is poor is the small value, otherwise it is the large value. The spraying method can be continuous spraying of cyanide solution or intermittent spraying. Intermittent spraying is beneficial to oxygen supplement and leaching of gold and silver. Spray cyanide solution for 2 hours, stop for 1 hour and then spray again.
When spraying alkaline cyanide solution, you should always check whether the nozzle pipe is blocked, and take measures to spray the solution to every place where it cannot be sprayed, so as to ensure the leaching rate of silver.
Adding an anti-scaling agent to the cyanide leach solution can prevent scaling of sprinkler pipes and ore piles.
heap leaching time
Depending on the ore properties and particle size, heap leaching usually takes 1 to 2 months, and for elderly individuals, up to 3 months. Gold concentrations in effluents below 0.1 g/m3 can be stopped by spraying.
By using carbon adsorption method, zinc replacement method, direct electrowinning and other methods, gold and silver are recovered from the leached gold and silver precious liquid.