The decantation washing method is widely used in North America, and it can be classified into a batch decantation washing method and a continuous decanting washing method.
First, the intermittent decantation washing method.
Intermittent decantation washing is usually used in combination with intermittent agitation cyanation. One method of operation it is clarified cyanide slurry tank after clarification by siphon with an upper float extracted supernatant containing gold recovery of gold send replacement, withdrawing the remaining thick slurry was stirred tank leaching dilute solution was added NaCN leaching again . The second method is to feed the cyanide slurry into a thickener, and the gold solution produced by the overflow is sent to the replacement gold. The thick slurry in the thickener is pumped to the stirring leaching tank and the NaCN dilute solution is used for leaching again. The secondary leached slurry is then sent to a clarification tank or a concentrator for further processing. This is repeated several times until the gold in the lotion reaches a trace amount. The gold-containing solution produced by the second leaching operation usually contains less gold and can be used for primary leaching of the next batch of raw materials, and the third leaching solution is used for secondary leaching of the next batch of raw materials. These solutions are continuously used until the gold concentration reaches a specified concentration and then the precipitated gold is sent.
The intermittent decantation washing method has few industrial applications because of the long working time, the large amount of solution used, and the large equipment footprint.
Second, continuous decantation washing method.
The continuous decantation washing method is one of the methods widely used at home and abroad. It is based on the principle that the slurry and washing liquid are reversely moving, and is called the continuous countercurrent decantation washing method in foreign countries (Fig. 1). In this method, the slurry and the washing (lean) liquid are fed into the thickener from the opposite direction and flowed into the next-stage thickener to realize the washing and solid-liquid separation of the slurry. Therefore, the thickener is the main equipment for continuous countercurrent decanting operation. To this end, the largest concentrator that has been used abroad has a diameter of 150 to 180 m. The concentrators used are single-layered and multi-layered. The continuous countercurrent decanting washing process and solution balance of a three-stage single-layer concentrator in a gold processing plant in China for daily processing of 100t ore are shown in Fig. 2.
Figure 1 Typical flow chart of continuous countercurrent decantation washing
Figure 2 Three-stage continuous countercurrent decanting washing process and solution balance in a plant
Due to the presence of large area single concentrator, and the slurry pump to be repeatedly sent Yang and other shortcomings, so many mineral processing plant are two to five concentrator assembly into a multilayer concentrated machine. Many of the gold selection plants in China are commonly used 2 to 3 layer thickeners (Figure 3). The continuous washing process of a three-layer concentrator in a cyanide plant is shown in Figure 4. The ore used for cyanidation in the plant is 88%-0.037mm, the concentration of ore is 27.8%, the concentration of ore is 37.72%, and the recovery rate of gold is 98.86%.
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