How to Upgrade Gold Concentrate Purity in Refractory Ores?
Upgrading gold concentrate purity in refractory ores is a challenging process due to the presence of impurities, native minerals, and refractory characteristics such as sulfides, carbonaceous matter, or silicates, which encapsulate the gold. The process requires a series of advanced metallurgical techniques. Below are some commonly used strategies and methods for upgrading gold concentrate purity:
1. Pre-Treatment of Refractory Ores
Since gold encapsulated in refractory ores cannot be easily extracted, specific pre-treatment methods are required, including:
- 焙焼:
- The ore is heated at high temperatures to oxidize sulfides, arsenic, and other impurities. This makes the gold more amenable to leaching.
- Example: Sulfides (pyrite and arsenopyrite) are oxidized to sulfur dioxide (SO₂) during roasting.
- 圧力酸化法 (POX):
- High-pressure and high-temperature oxidation is used in an autoclave with oxygen to break down sulfide matrices.
- Bio-oxidation (BIOX):
- Utilizes bacteria to selectively oxidize sulfide minerals without the need for high energy inputs.
- 超微粉砕:
- Reduces ore particle size to increase gold liberation and improve leaching efficiency.
2. 重力選鉱
- For refractory ores containing free gold, gravity separation is often an effective pre-concentration step.
- Techniques include:
- 振動テーブル
- Knelson or Falcon concentrators
- スパイラル濃縮機
- Use gravity separation to separate high-density gold particles from gangue and impurities.
3. フロート選鉱
- When gold is associated with sulfide minerals (pyrite, arsenopyrite), flotation can be used to enrich the concentrate.
- Collectors such as xanthates or dithiophosphates are employed, along with frothers, to selectively float gold-bearing sulfides while suppressing non-valuable gangue.
- The flotation concentrate is further processed through other methods like roasting or pressure oxidation to recover gold.
4. Leaching and Cyanidation
- For higher purity, gold concentrates can be subjected to hydrometallurgical methods, such as leaching.
- シアン化物浸出:Gold is dissolved into a cyanide solution during subsequent refining processes. Pre-treated refractory concentrates improve leach recovery.
- チオ硫酸塩浸出:An alternative to cyanidation, suitable for ores with high copper content or preg-robbing carbonaceous material.
5. Carbon-In-Leach (CIL)/Carbon-In-Pulp (CIP) Processes
- The pulp is combined with activated carbon, which adsorbs gold from the solution.
- Suitable for higher purity recovery after refractory ore pre-treatment.
6. Calcination (for Carbonaceous Ores)
- For refractory ores containing organic carbonaceous matter, calcination at high temperatures can destroy the carbon and liberate gold.
- This prevents gold from being adsorbed during leaching (a phenomenon called preg-robbing).
7. Clean-Up Processing
- 磁気分離:
- Removes magnetic impurities (e.g., iron) from the concentrate.
- 精製:
- After primary gold recovery processes, the concentrate is refined using methods such as chlorination, smelting, or electrowinning to produce a higher-purity gold.
8. Consider Hydrothermal Processes
- High-temperature chloride or alkaline solutions can dissolve impurities while retaining gold, enhancing concentrate purity.
Integrated Approach:
For best results, an integrated combination of processes may be used. For instance:
- Combine flotation to produce a gold-rich sulfide concentrate.
- Roast or bio-oxidize the concentrate to liberate gold, followed by cyanidation.
9. Environmental Concerns
- Ensure compliance with environmental regulations during processes like roasting, cyanidation, and POX, which may produce toxic emissions or waste.
By combining suitable techniques based on the mineralogical and chemical characteristics of the ore, a more efficient and economical process for upgrading gold concentrate purity in refractory ores can be designed.
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