Many people think that gold mining is when miners use pickaxes to dig out gold nuggets from mines. In reality, gold mining is more like a sophisticated chemical separation process. In one ton of gold ore, the gold content is often only a few grams or even lower. To separate these rare gold from a large amount of rocks, the help of various mineral processing agents is indispensable.
Today, we will talk about several commonly used reagents in gold ore dressing and their respective functions.
After the gold ore is excavated from the mine, the gold is embedded in a large amount of waste rock. Directly taking it for smelting has high cost and low efficiency. The purpose of mineral processing is to enrich gold from waste rock using physical or chemical methods, forming a "concentrate" with high gold content, and then proceed to the next step of smelting.
There are currently two mainstream mineral processing methods:Flotation methodandLeaching methodThe drugs used in the two methods are completely different.
The flotation method can be understood as follows: grinding the ore into fine powder, pouring it into water and stirring it, then adding several chemicals to the water and filling it with air to produce a large number of bubbles. Mineral particles containing gold will adsorb onto bubbles and float to the surface of the water; Waste rocks that do not contain gold sink to the bottom of the water. Scrape the water surface with foam, and you will get a concentrate with much higher gold content.
The drugs used in this process can be divided into three roles:
1. Collector - helps gold "grab" bubbles
Most mineral surfaces are naturally hydrophilic and do not actively lean towards bubbles. The function of a collector is to selectively adsorb onto the surface of gold bearing minerals, making them hydrophobic and easier to adhere to bubbles.
The most commonly used collector in gold flotation isxanthateNamed after its pale yellow powder appearance. According to the length of the carbon chain, the Huangyao family has different members: short chains have relatively mild capture capabilities, while long chains have stronger capture capabilities and are suitable for difficult to select ores. In actual production, mixing two or more collectors often yields better results than using a single variety.
2. Foaming agent - creating stable bubbles
Just having a collector is not enough, there needs to be enough and stable bubbles to 'transport' mineral particles. Foaming agents can reduce the surface tension of water, making it easier for the filled air to form small bubbles and less prone to rupture.
The most commonly used foaming agent isPine alcohol oil(also known as No. 2 oil), with low price and stable performance. In addition, there are also varieties such as ether alcohols.
3. Adjuster - Adjusting the flotation environment
The adjusting agent does not directly participate in capturing gold, but is responsible for optimizing the conditions of the entire flotation process. The main tasks include:
Adjust acidity and alkalinityAdd lime or sodium carbonate to keep the slurry in the appropriate pH range
Inhibit unwanted mineralsSome minerals (such as arsenic compounds) do not want them to float up together, so inhibitors are added to "hold" them down
Activate target mineralsSome gold is wrapped in other minerals and the flotation effect is not good, so activators are added to help it be exposed
The three types of medicines each perform their own duties and work together to enrich gold.
The leaching method is another approach: using a solution of a drug that can dissolve gold, directly spraying it onto the ore, allowing the gold to dissolve from a solid to a liquid, and then collecting the gold containing solution to extract the gold through activated carbon adsorption or zinc powder displacement.
This method is particularly suitable for processing low-grade gold ores or ores with unsatisfactory flotation performance. When applied on a large scale, the "heap leaching" process is often used - the crushed ore is piled up into a huge heap, an anti-seepage bottom pad is laid, and a spray system is used to evenly spray the chemical solution on the surface of the heap. During the penetration process of the chemical solution, the gold is dissolved and collected after flowing out from the bottom.
Leaching agents are mainly divided into three categories:
1. Sodium cyanide
Sodium cyanide is the oldest and most widely used reagent in the field of gold leaching, with over 80% of gold mines worldwide using cyanide for gold extraction. Its advantages are good leaching effect and relatively low cost. But the downside ishighly toxic——The lethal dose to humans is very low, and once leaked, it will bring serious environmental and safety risks. Therefore, there are strict regulatory requirements for the production, storage, and transportation of sodium cyanide.
2. Environmentally friendly beneficiation agent
In response to the safety hazards of sodium cyanide, researchers have developed environmentally friendly mineral processing agents. The design concept of this type of product is to "lock" the cyanide group, which plays a key role, in the molecular structure in the form of chemical bonds. Under normal conditions, it is not easy to release highly toxic components that can escape, but it can effectively dissolve gold in a gold immersion environment.
Compared with sodium cyanide, the advantages of environmentally friendly beneficiation agents are: significantly reduced toxicity (belonging to ordinary cargo transportation, no need for toxic approval procedures); Can directly replace sodium cyanide without the need to modify existing equipment and process flow; The cost of treating tailings after leaching is relatively low.
3. Non cyanide agents
Non cyanide agents include thiourea, thiosulfates, etc., which are completely cyanide free and theoretically more environmentally friendly and safe. However, there are still some bottlenecks in this type of technology at present: some drugs consume large amounts, resulting in high costs, while others require acidic or high-temperature conditions and have high equipment requirements. Therefore, large-scale industrial applications have not yet been achieved.
Flotation and leaching are not an either or relationship, but rather the selection of appropriate methods based on the properties of the ore. Sometimes, they are also used in combination.
Flotation methodSuitable for ores where gold and sulfide minerals coexist, high-grade gold concentrate can be obtained through flotation. The flotation speed is fast and the cycle is short, but it requires grinding the ore very finely, resulting in high energy consumption.
Leaching methodSuitable for low-grade oxidized ore or flotation tailings, with a simple process and low investment, but a long leaching cycle (heap leaching generally takes 30-90 days).
Joint processFor difficult to process gold mines, sometimes gold concentrate is obtained through flotation first, and then leached. The combination of the two can improve the overall recovery rate.
Someone may ask: Is it cost-effective for environmentally friendly mineral processing agents to be slightly more expensive than sodium cyanide?
The answer depends on the overall cost. Although sodium cyanide has a low unit price, there are many hidden costs during its use: it requires the construction of a dedicated warehouse that meets security standards, transportation requires public security approval and specialized vehicles for hazardous chemicals, operators need professional training and protective equipment, and the tailings also need to be treated harmlessly. Taking all these costs into account, the overall cost of environmentally friendly beneficiation agents is often not higher. More importantly, it significantly reduces safety risks and environmental compliance pressures.
There are currently three clear development directions for the gold ore dressing and pharmaceutical industry:
Firstly, the proportion of environmentally friendly pharmaceuticals is increasing. 随着环保政策趋严，越来越多的矿山企业开始从氰化钠转向环保选矿剂，这个替代过程还在持续推进中。
Secondly, medication plans are becoming increasingly "customized". 不同矿山的矿石成分差异很大，标准化的药剂配方往往不是最优解。好的供应商会根据具体矿石的特性，提供针对性的药剂方案。
Thirdly, the service model is undergoing a transformation. 优秀的厂商不只销售药剂产品，还会提供从矿石检测、药剂选型到现场调试的全流程技术支持。
From ore to gold, a series of complex physical and chemical processes are involved. Collectors, foaming agents, adjusters, extractants... each agent plays a specific role in its own process. The flotation method allows gold containing minerals to "float" up, while the leaching method allows gold to "dissolve" out. Both methods have their own applicable scenarios. The popularization of environmentally friendly mineral processing agents is moving gold production towards a safer and greener direction.
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