Gold Slime Treatment and Smelting in Containerized Cyanide Leaching Plants

Why the Desorption and Electrolysis Section Matters

In a cyanide gold leaching plant, activated carbon is commonly used to adsorb dissolved gold from the leaching solution. After adsorption, the loaded carbon must be treated by desorption to release the gold into a rich solution. Then electrolysis is used to recover gold from the solution and form electrolytic gold slime.

This section connects the leaching stage with the final metal production. A stable desorption and electrolysis system can help reduce gold loss in carbon and solution, improve recovery performance and make the following smelting work easier.

If the layout is not reasonable, operators may face problems such as difficult material handling, unstable operation, high energy consumption and more maintenance work. For this reason, the desorption, electrolysis and smelting section should be considered as a complete process, not as several separate machines.

 

Common Problems in Small and Medium Gold Recovery Plants

Many small and medium gold plants do not have enough space, skilled operators or complete workshop conditions. Some projects are located in remote mining areas where transportation, installation and construction are difficult.

In these cases, a traditional fixed plant may take a long time to build and may require more civil work, more workers and higher investment. Another common problem is that different process sections are purchased separately from different suppliers.

Leaching equipment, desorption columns, electrolysis cells, furnaces and control systems may not match each other well. This can lead to lower efficiency, more site modification work and longer commissioning time.

For many 10tpd mobile cyanide leaching plant, a compact containerized design can be more practical than building a large traditional workshop from the beginning.

The Role of Gold Slime Treatment Before Smelting

After electrolysis, the gold is usually obtained as electrolytic gold slime. This material is not always ready for direct casting, because it may still contain moisture, residual chemicals, silver, copper and other base metals. Proper pretreatment is necessary before smelting.

The first step is washing. Gold slime should be washed carefully with clean water to remove residual cyanide and soluble impurities. This step is very important for operation safety, especially before any acid treatment.

In some plants, nitric acid wet pretreatment is used to remove base metals from gold slime. Dilute nitric acid can dissolve metals such as silver and copper, while gold remains mainly in the solid residue. The reaction should be controlled carefully, with small-batch feeding and proper temperature control, to avoid violent reaction, overflow or unnecessary metal loss.

Typical Gold Slime Pretreatment Steps

1. Wash electrolytic gold slime with clean water to remove residual cyanide.
2. Add dilute nitric acid slowly for initial impurity removal.
3. Heat and stir the material after the reaction becomes stable.
4. Filter to separate the solid gold-bearing residue from the liquid.
5. Wash the residue until it is close to neutral.
6. Dry the purified gold slime before furnace smelting.

Medium-Frequency Furnace Smelting for Gold Slime

After washing, impurity removal, filtration and drying, the purified gold slime can be mixed with flux and sent to the smelting stage. A medium-frequency induction furnace is widely used for this work because it heats fast, offers stable temperature control and is suitable for melting precious metal materials.

During smelting, the dried gold slime is usually mixed with flux such as borax. The furnace temperature is raised to about 1200–1300℃ so that the gold-bearing material can melt completely. The flux reacts with remaining impurities and forms slag.

After the molten material stands for a short time, slag is removed carefully. Then the molten alloy is poured into a mold and cooled to form crude gold ingots.

Slag removal is an important operation. If slag is discharged too quickly or without proper control, part of the molten gold may be carried out with the slag. Good operating practice can reduce this loss and improve the final recovery result.