On methods for recovering heavy metals from electroplating sludge

Landfilling is wasteful and also causes severe environmental pollution. Out of a sense of responsibility to future generations. Solutions should be explored. It is unknown what the composition of the material is, and what the sulfuric acid leaching rate is. Can acid leaching, oxidation for iron removal, and extraction processes be used to recover copper and nickel?

Acid leaching is used for such sludge; firstly, it results in high acid consumption, and secondly, the vast majority of metals (except calcium) are leached into the solution, with the concentrations of iron and chromium in the solution being much higher than those of copper and nickel. Therefore, using the conventional acid leaching method presents significant difficulties for subsequent impurity removal: firstly, the issue of acidic pressure filtration is difficult to resolve; secondly, the amount of slag generated by removing iron and chromium is large, resulting in nickel losses of over 10%; thirdly, the cost aspect is a major obstacle – even if 100% recovery is achieved per ton of material, only a few dozen kilograms of copper and nickel are obtained. Therefore, the acid leaching method is not very feasible.

Could we dehydrate first and then carry out acid leaching? This way, the acid consumption should be reduced. Another question: at what level of metal content in electroplating sludge is it worthwhile to carry out recovery?

Dehydration has little to do with acid consumption； Based on current copper and nickel prices, it is estimated that at least one of the nickel or copper base grades needs to reach over 8% to be worthwhile; in the past, when nickel prices were above 100,000, a grade of not less than 5% was required, but now it is difficult to even achieve break-even.

Back to floor 4: It depends on what method is used for recycling.

The nickel- and copper-containing sludge is leached with acid to recover copper and nickel by extraction. However, the sludge containing nickel, copper, zinc, and chromium that I’ve encountered recently has such low concentrations that it’s not economically viable to process it using conventional methods. If anyone has any good suggestions, I would be grateful if you could share them. :lol

Personal idea: First, carry out dehydration and drying treatment, which can be achieved using existing rotary kilns; thereafter, apply separation methods. There are already reports on the use of separation methods for processing refractory copper oxide ores (with 2-3% copper content), allowing for the production of copper-nickel concentrate through mineral processing. A key factor here is the change in the state of chromium during the separation process; that is, if it becomes hexavalent, it will cause water pollution during the mineral processing stage and make it difficult to handle. Therefore, the change in chromium during separation determines its technical feasibility. Furthermore, it is necessary to further verify relevant technical indicators such as recovery rate and concentrate enrichment ratio, as well as costs such as fuel and auxiliary material consumption. It is estimated that a cost of 400–500 yuan per ton or less would be acceptable. Furthermore, the separation method requires a large initial investment and needs to be scaled up. Article excerpt: The analysis-flotation method is a technique that combines pyrochemical treatment with flotation. For example, in the separation-flotation process for refractory copper oxide ores, the ore is crushed to a certain particle size and then mixed with a small amount of table salt (0. 1-1. 0%) and coal powder (0. 5-2. (0%), and by heating it in an oxygen-free environment to around 900 degrees, copper in the ore precipitates on the surface of the carbon particles in its metallic form. After cooling the roasted ore in an oxygen-free environment, it is ground and subjected to flotation, thereby yielding copper concentrate. The greatest advantage of the separation-flotation method is its ability to handle ores that cannot be processed using conventional mineral processing techniques; it allows for the comprehensive recovery of useful metals from these ores. For example, in copper ores, when the ore contains large amounts of malachite, cuprite, and bound copper, or when it contains a high amount of ore mud, flotation often yields poor results for such ores, whereas separation methods are more effective. The separation method can also handle mixed ores of copper oxide and copper sulfide ores, and enable the comprehensive recovery of useful metals such as gold, silver, and iron. Furthermore, compounds of several metals such as gold, silver, nickel, aluminum, cobalt, antimony, palladium, bismuth, and tin are easily reducible and readily form volatile chlorides, making them suitable for treatment by separation methods. The disadvantage of the separation method is its high cost, significant capital investment, and high production expenses. It is estimated that the capital investment for the separation method is about twice that of a flotation plant with similar capacity, and the production costs are also 2 to 3 times higher. Therefore, when using the separation method to process refractory copper oxide ores, it is considered that a copper content in the ore of over 2% is required to achieve good economic results. Therefore, the separation method is used only to deal with ores that cannot be processed by other methods. Therefore, before adopting this method, a thorough study of the ore to be processed should be conducted; if it can be processed by other methods, the separation method should not be used. (end) http://cm.newmaker.com/art_24577.html

Leaching—impurity and iron removal—filtration—ion exchange—salt products.

1. Sulfuric acid leaching; the leachate contains copper, nickel, chromium, and iron, with calcium and other impurities removed ； 2. Extracting copper ； 3. Acid is recovered by low-pressure distillation, with nickel, chromium, and iron as the residues ； 4. Nickel, chromium, and iron residues are used as raw materials for stainless steel. Key: Control of chromium ion valence; use of nickel, chromium, and iron residues in the formulation and manufacturing process of stainless steel.

The method is great, support it! However, the moisture content of such electroplating sludge is generally above 70%, and the total amount of metal ions in the leachate is only a few dozen grams per liter. If it is concentrated, there may be issues such as prolonged processing times and high energy consumption. Moreover, the residue still needs to be neutralized with alkali before precipitation – so what value does such a product have if it is sold to those who produce stainless steel? When it comes to copper extraction, iron is more difficult to extract, and the associated costs may be higher. Through acid leaching, such electroplating sludge is neutralized with lime; approximately 30-50% sulfuric acid is consumed per ton of sludge. At the current price of sulfuric acid, which is around 200 yuan per ton, the extraction cost is about 150 yuan. Adding in costs related to concentration and other factors, the total cost is estimated to be around 800 yuan per ton, which raises questions about its economic viability.