Zinc cementation gold extraction is a classic and widely used hydrometallurgical technique, mainly applied to recover gold by cementation from gold-bearing cyanide leach solution.
Basic Principle
Based on the metal activity series, zinc is more reductive than gold. It can reduce gold ions in cyanide solution to metallic gold, which precipitates out, while zinc itself is oxidized and dissolved to form zinc cyanide complex ions with cyanide ions.The reaction proceeds spontaneously in an alkaline cyanide solution and has a large equilibrium constant.
Application Conditions
Applicable ores: Suitable for oxidized ores and free-milling gold ores. Gold minerals in such ores readily react and dissolve with cyanide, providing favorable conditions for subsequent cementation and achieving high gold recovery.This method offers unique advantages for high-silver gold ores, enabling simultaneous silver recovery to produce gold sludge and silver-rich products, thereby improving the comprehensive utilization of precious metals.
Process Flow
Step 1: Raw Material Treatment
The gold-bearing cyanide pregnant solution often contains impurities such as slime, undissolved mineral particles and organic matter, which hinder the contact between zinc powder and gold ions, reduce the displacement efficiency, and even cause equipment blockage. Therefore, purification is required to ensure the stable operation of subsequent processes.
The gold-bearing cyanide pregnant solution first enters the filter press, where slime, suspended solids and other impurities are removed under pressure to obtain purified pregnant solution. The purified solution is then transferred to the purified pregnant solution tank for storage, providing a stable and clean feed solution for subsequent processes. The purified pregnant solution flows out from the upper side outlet of the tank, with flow regulated by a butterfly valve, and enters the next stage.
Step 2: Deoxidation Treatment
Dissolved oxygen preferentially reacts with zinc powder, resulting in zinc powder consumption, and re-oxidizes and redissolves the displaced metallic gold into the solution, lowering the gold recovery rate. Therefore, deoxidation treatment must be performed on the purified pregnant solution.
The purified pregnant solution passes through a butterfly valve and enters the deaeration tower. A vacuum pump, supported by a circulating water tank, provides vacuum power to extract and remove dissolved oxygen from the pregnant solution, preventing oxidation of zinc powder and redissolution of gold. A level gauge monitors the liquid level in the tower in real time to avoid backflow of pregnant solution into the vacuum pump, and a negative pressure gauge monitors the vacuum degree to ensure satisfactory deoxidation performance. The deaerated pregnant solution flows out through a butterfly valve and is delivered by a jet pump (based on jet flow principle) to the zinc powder mixing stage.
Step 3: Zinc Powder Mixing
The zinc powder feeder quantitatively feeds zinc powder into the zinc powder mixing tank, with an activator added simultaneously. The mixture is stirred inside the tank to form a highly active zinc powder suspension. The zinc powder suspension flows through the outlet ball valve of the mixing tank for flow regulation, and mixes with the deaerated pregnant solution at the inlet of the displacement pump. The combined mixture enters the displacement pump and is pressurized and delivered to the subsequent process.
Step 4: Displacement and Precipitation
The mixed solution is pressurized and conveyed by the displacement pump, passes through a flow meter for flow monitoring and a pinch valve for on-off control, and then enters the filter press. In the multi-chamber structure of the equipment, zinc powder reacts with gold ions through displacement; gold is reduced to gold sludge and precipitated, while zinc powder dissolves into the solution. A sampling ball valve enables online sampling to detect the grade of gold sludge and gold content in the barren solution. A pressure gauge monitors the internal pressure of the equipment in real time to ensure safe and stable reaction.
Step 5: Gold Sludge Separation
After displacement and precipitation, the filter press completes solid-liquid separation simultaneously: gold sludge is retained on the filter cloth and taken out for the smelting process afterward. The barren solution discharged from the filter press is treated by washing and water treatment, then reused in the production system to realize material recycling.
Advantages
Simple operation and easy-to-master process flow, with moderate technical requirements for operators.
Fast cementation and high gold recovery rate.
Low zinc powder price and low material cost.
Lower environmental pollution compared with some chemical methods.
Method Comparison
1. Compared with conventional methods: Zinc cementation features simple operation, fast reaction, and high gold recovery (usually over 99%).Zinc powder is relatively inexpensive, providing obvious material cost advantages, with lower environmental pollution.
2. Compared with other gold extraction methods (eg. CIP, RIP): Zinc cementation has a simpler flow sheet, lower equipment investment, and is more environmentally friendly.Although CIP achieves high recovery, it involves complex processes, higher capital and operating costs, and carries cyanide pollution risks requiring strict wastewater control and treatment.
3. Compared with physical methods (eg. gravity separation): Gravity separation is suitable for coarse-grained gold ores but performs poorly for fine-grained gold, with limited application.Zinc cementation has a much wider application range and can treat various types of gold ores.
At present, zinc cementation gold extraction remains a widely adopted cyanide-based gold recovery method for treating flotation gold concentrates.It plays a critical role in the post-cyanidation leaching stage of gold ore processing.
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