The extractant is selected in the leaching-extraction-electrowinning process, and the various conditions and parameters of the leaching liquid component, the extracting agent, the extraction and the back extraction, and the components of the electrowinning rich liquid and the residual liquid interact with each other and are mutually restricted. In the design of a leaching-extraction-electrowinning plant, the first step is to conduct a leaching test with the actual ore to obtain the average composition of the leaching solution, mainly copper concentration and pH, followed by iron concentration. Once the average composition of the leachate has been determined, the extractant and its concentration required for the extraction system can be selected. The basic principle of calculation is that the mass flow of copper in the process of leaching, extraction and back extraction and electrowinning should be balanced during steady state operation. Since the electrowinning is a relatively stable process, the concentration of copper and sulfuric acid in the electrolyzed liquid and the liquid is set first, so that the copper concentration of the organic phase after stripping is easily determined. Then, the parameters that need to be determined in the stripping process leave the two phase ratio.
Although there are many kinds of extractants, new extractants with aldoxime as the main component are generally used, such as Acorga M5640, M5615, M5397, P-5100, PT-5050 and Henkel's LIX984, LIX973, LIX931, and LIX860. , L1X84, LIX622 series and its improved models. Although the parameters indicated in the technical specifications of the extractants of various manufacturers are not the same, they generally include the maximum load capacity, transport capacity, and extraction and stripping isothermal equilibrium points of the extractant.
Extraction Process Design The extraction process design is to determine the operating parameters such as extractant concentration, comparison, and number of stages. The operating parameters were calculated by taking a solution containing 1.2 g/L of copper and pH=1.8 as an example. It is assumed that LIX984 or 984N is selected as the extractant. According to experience, the two-stage countercurrent extraction, the first-stage stripping process can be compared to 1:1 when performing the extraction calculation. According to the specification of the extractant, when the concentration is 10% (v/v), the net transport capacity is 2.7 g/L, the maximum load is 5.1 to 5.4 g/L, and the back extraction isothermal equilibrium point is 1.8 g/L. The copper is required to be transferred at a concentration of 5% (v/v), and it is estimated that half of the organic phase copper concentration of the stripping isothermal equilibrium point is 10%, that is, 0.9 g/L. Thus, the copper concentration of the loaded organic phase should be 1.2 + 0.9 = 2. lg / L, which is 81% of its maximum load. This is appropriate, too high, there is no room for the extraction operation; too low, the extraction agent utilization is too low. Therefore, it is generally considered that the operating load is 80% to 85% of the maximum load. When the production plant is measuring the properties of the extractant, the electrolyzed lean liquid is set to Cu30g/L, H 2 S0 4 180g/L; the rich liquid is Cu45g/L, and the stripping is compared with A/0=7.1. This determines all operating parameters for extraction and stripping.
Jielikon has developed a computer program called Minchem that performs process calculations on the extraction-reverse extraction process for a given set of operating parameters, evaluates the current operating state, and can also extract using known conditions. Optimize the design. For example, a copper concentration of liquid feed user is 2.5g / L, pH = 2.3, the organic phase was 10% Acorga5640- coal oil. Electrolyzed lean liquid for reverse extraction Cu30g/L, H 2 S0 4 180g/L; electrolytic feed liquid containing copper 45g/L. Minchem's isotherm module calculates the extracted and stripped equilibrium isotherms. For example, the plant is a secondary extraction primary extraction, and it is known that the extracted two phases are 0/A =1/1, the mixing efficiency of the mixing-clarification tank is 90%, and the extraction is 95%. Then, the program's "flowchart drawing and calculation module" can calculate the two-phase concentration and the counter-extraction flow as shown in the following figure.
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The calculation results show that the direct yield of copper is 93.3%. The user can change the above-mentioned parameters such as the stage efficiency, the flow ratio, or even the number of stages or select other parameters to perform calculations to compare the operation results under different conditions and determine the optimal operation parameters. Recently, the improved Minchem program uses a user-window interface for easy operation. Moreover, the calculation results, including the isotherms, can be printed.
Although the calculated operating parameters can be used as the basis for actual operation, it must be adjusted according to the change of copper concentration and pH value of the liquid during the actual operation. In the case where the composition of the feed liquid does not change much, the direct yield of copper can be ensured by changing the ratio of the two-phase flow. If the concentration of the feed liquid changes too much, the concentration of the extractant can be adjusted when the extractant is added.
However, if the feed concentration is high, there are special requirements or processes, should be designed, such as the use LIX84 design extractant in the extraction of copper from a copper-containing gold concentrate leaching calcine fluid flow according to the actual situation A 4-stage extraction reduces the copper content in the raffinate to below 0.1 g/L, and the subsequent removal changes the usual practice of returning to leaching. In order to avoid the adsorption of organic matter in the raffinate on the leach residue to affect cyanide gold extraction [1] .
Chloride ion erodes lead anode. If the liquid contains more than 3g/L of chloride ion, some of it will enter the organic phase during extraction. A washing stage should be set to wash away the impurities and prevent it from entering the electrolyte. Nitrate and divalent manganese ions also have an adverse effect on the electrowinning, and also need to be washed when the concentration is high.
Industrial extraction runs with a small number of copper extraction stages and large equipment. In addition to the common points of extraction operation, such as flow control of various solutions, there are several points to be paid special attention to.
Selection of the continuous phase When the two phases are mixed, the dispersed phase always produces some very small droplets which cannot be separated from the continuous phase in the clarification tank, and the entrainment proceeds to the next step. Although the extractant has a very high selectivity to copper, if the organic phase entrains the liquid, it can also transfer impurities to the stripping solution, which adversely affects the quality of the copper. The entrained organic phase is lost with the aqueous phase and also increases production costs. In principle, the organic phase of the loading phase of the loading phase should be kept continuous in order to reduce the aqueous phase entrained in the organic phase. Conversely, the raffinate outlet stage organically corresponds to a continuous phase to reduce the loss of the organic phase. Therefore, the continuous correspondence of the two-stage extraction is different. If the stripping is only one stage, it is better to continue the organic phase. This keeps the electrolyte clean and ensures the quality of the copper. The high concentration copper solution entrained in the stripping organic phase can be recovered during extraction.
One method of maintaining the phase continuity is to stir the paddle in the dispersed phase when starting the mixing tank, and then to keep the volume of the continuous phase in the mixing tank larger than the dispersed phase. In the industrial process, the latter is the main method. Even if the selection of the continuous phase is correct when driving, "phase inversion" sometimes occurs during operation, that is, the continuous phase changes to the dispersed phase, and the dispersed phase becomes the continuous phase. Therefore, continuous phase monitoring is required during operation. The most commonly used identification method is to measure conductance, and the continuous conductivity of the aqueous phase is higher than that of the organic phase.
It has been mentioned before the entrainment is reduced that the entrainment is due to the partial dispersion of the droplets being too fine when the two phases are in contact. The finer the droplet, the slower the process of separating from the other phase by gravity. During the residence of the clarification tank, many droplets are too late to be taken out and taken to the next stage. Therefore, to reduce the entrainment, it is fundamentally to avoid the droplets being too finely dispersed. When the two phases are in contact, reducing the droplet diameter is advantageous for mass transfer. However, the droplet diameter is in a certain distribution state, and the droplet diameter should be made as uniform as possible, or the distribution is narrower, and the fine droplets are reduced. The main cause of excessive distribution is the design or improper operation of the paddle. If the shear force of the blade is too large, fine droplets will be produced. Some of the mixing and clarification slots are improperly connected to the opening of the tube, and the air is drawn into the mixing chamber, and sometimes it is not. This will cause a tidal surge in the mixing chamber, and as a result, the two-phase dispersion state will also change, resulting in excessive droplets. At the same time, a three-phase mixture of water, oil, and air can also result in a three-phase emulsion. Emulsification will result in severe entrainment.
references:
1.Zhu Tun, Zhou Xiexi, A New Process for Copper Recovery in A Gold Refinary, Proceedings of ISEC'96, ed. by DC Shallcross, R. Paimin and L M. Prvcic, Vol. I, 1996. 581-586
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