New cobalt removal agent AnBm removes cobalt from wet zinc sulphate solution

In the wet zinc smelting process, cobalt is one of the most important impurities that harm zinc electrowinning. During the electrowinning process, the overpotential of hydrogen on cobalt is small, the presence of cobalt promotes hydrogen discharge, and the cathode potential is shifted positively, and the overpotential is reduced. As the electrowinning progresses, the deposit becomes more and more porous, the cathode zinc is dissolved, the current efficiency is lowered, the electric energy consumption of zinc is increased, the zinc stripping is difficult, and the zinc yield is lowered. Therefore, it is necessary to remove cobalt to a lower concentration before zinc electrowinning. At present, the main methods for removing cobalt in wet zinc smelting include active zinc powder method, xanthate cobalt removal method, solvent extraction method, and β-naphthol method. Method of treating waste water of heavy metals present Reference experiment, the large number of experiments based on the use of a novel inexpensive cobalt removal agent AnBm, cobalt removal process so easy, and without introducing new impurities detrimental to the process, no exhaust gases, The effect of removing cobalt is good.

First, the test part

(1) Test materials

The test solution was taken from a zinc liquid smelting plant in Yunnan, which is a copper and cadmium removal liquid. The composition is shown in Table 1; Fe ^{3 +} standard solution: 1 g/L, prepared from analytical pure sulfuric acid high iron ; Co ^{2 +} standard Solution: 5 g / L, prepared from analytically pure cobalt sulfate; concentrated sulfuric acid: analytically pure, 17.93 mol / L; cobalt removal agent AnBm, 99%.

Table 1 Main components of zinc sulfate solution mg/L

(2) Test methods

The test was conducted using a single factor test. Pour 100 mL of working solution into a 250 mL high-type beaker, heat in a water bath, and mechanically stir. In addition to the cobalt liquid filtration, the mass concentration of cobalt, iron and zinc in the filtrate was measured, and the removal rate of each element was calculated.

Test equipment: HH-2 digital display constant temperature water bath, temperature control accuracy ± 1 ° C; JJ-1 electric mixer; precision pH test paper and lightning magnetic pHsj-3F laboratory pH meter SHB-III A type circulating water multi-purpose Vacuum pump.

The determination of Co ^{2 +} in the solution was carried out by nitroso-R salt spectrophotometry (Model 722 spectrophotometer); the determination of Zn and Fe was carried out by flame atomic absorption spectrometry standard curve method (Shimadzu AA6300 atomic absorption spectrophotometer).

Second, the principle of testing

The cobalt removal agent AnBm contains a xanthogen group, which can form a precipitate with cobalt ions in the solution, and the solubility product of the trivalent cobalt salt of xanthogen is one hundred thousandth of the divalent cobalt salt, so When cobalt is removed to a lower concentration, an oxidizing agent should be added to oxidize the divalent cobalt to trivalent cobalt. The test removes cobalt from the solution by adding an oxidizing agent followed by a cobalt removal agent.

Third, the results and discussion

The single factor test method was used to investigate the effect of the amount of oxidant added, reaction time, reaction temperature, addition amount of cobalt removal agent AnBm, and removal point of cobalt on the removal rate of cobalt.

(1) Effect of oxidant addition on cobalt removal rate

The oxidant is a solution prepared from analytical pure ferric sulfate. Take different volumes of 1g/LFe ^{3 +} standard solution, and dilute to 100mL with zinc sulfate solution after removing cadmium and copper. Other conditions: 0.32g of cobalt removal agent, temperature 75±1°C, reaction time 1h, solution pH 4. 45. The test results are shown in Figure 1.

Fig.1 Effect of oxidant Fe ^{3 +} mass concentration on drilling and iron removal rate

It can be seen from Fig. 1 that with the increase of Fe ^{3 +} addition, the cobalt removal rate increases rapidly; when the Fe ^{3 +} addition amount reaches 42 mg/L, that is, the Fe ^{3 +} addition amount is Co ^{2 +} completely oxidized to Co. ^{When the} theoretical amount of ^{3 +} is 1.7 times, the cobalt removal rate is 97.5%, and the cobalt concentration of the liquid cobalt is reduced to 0.7 mg/L or less after decobalting. Meanwhile, the iron as an oxidant is also precipitated, and the precipitation rate is nearly 100%. No new impurities were introduced into the solution.

(II) Effect of the addition amount of cobalt removal agent on the removal rate of cobalt

Fix other test conditions: add Fe ^{3 +} mass concentration to 42mg/L, temperature 75±1°C, time 1h, solution pH 4.35, constant volume volume 100mL, the effect of cobalt removal agent addition on cobalt removal rate test results Figure 2 shows.

Figure 2 Effect of cobalt removal agent addition on cobalt removal rate

It can be seen from Fig. 2 that the cobalt removal rate increases with the addition of the decobalting agent; when the mass concentration of the cobalt removal agent is 2.4 g/L, the cobalt removal rate is over 97%, and the cobalt concentration after decobalting is high. Reduced to below 0.7mg / L, fully meet the requirements of zinc.

(III) Effect of reaction temperature on cobalt removal rate

The decobalting agent was added in an amount of 0.24 g, Fe ^{3 + was} added to a mass concentration of 42 mg/L, the reaction time was 1 h, the solution pH was 4.47, and the volume was 100 mL. The effect of temperature on the removal rate of the drill was investigated at different water bath temperatures. The test results are shown in Figure 3.

Figure 3 Effect of temperature on cobalt removal rate

It can be seen from Fig. 3 that the cobalt removal rate increases rapidly with increasing temperature; when the temperature reaches 80 °C, the cobalt removal rate is over 97%, and the cobalt concentration after the precipitation of cobalt is as low as 0.8 mg/L; When the temperature was raised, the cobalt removal rate did not change significantly, and no cobalt reverse dissolution occurred.

(4) Effect of reaction time on cobalt removal rate

The decobalting agent is added in a mass of 0.24 g, the Fe ^{3 + is} added to a mass concentration of 42 mg/L, the solution pH is 4.37, and the volume is 100 mL.

The effect of reaction time on cobalt removal rate is 75±1°C, and the test results are shown in Fig. 4.

Figure 4 Effect of reaction time on cobalt removal rate

It can be seen from Fig. 4 that the reaction time has a great influence on the removal rate of cobalt: the precipitation rate of cobalt increases rapidly with the reaction 30 minutes before the reaction; the precipitation rate of cobalt increases slowly after 30 minutes of reaction; the concentration of cobalt in the solution after 60 minutes of reaction It has been reduced to 0.64 mg/L, and the cobalt removal rate is 97.4%. The reaction is almost complete.

(5) Effect of solution pH on cobalt removal rate

The decobalting agent was added with a mass of 0.24 g, a Fe ^{3 +} mass concentration of 42 mg/L, a constant volume of 100 mL, a temperature of 75 ± 1 ° C, and a reaction time of 1 h. The effects of different acidity on the removal rate of cobalt were investigated. The test results are shown in Fig. 5.

Figure 5 Effect of solution pH on cobalt removal rate

It can be seen from Fig. 5 that the cobalt removal efficiency is low when the acidity of the solution is high: the removal of cobalt is best when the pH is between 4.1 and 5. Too high a pH will reduce the cobalt precipitation effect because at high pH conditions, Fe ^{3 +} and Zn ^{2 + are} easily hydrolyzed, directly reducing the effect of the cobalt removal agent. The pH of the zinc sulphate neutral leachate in the wet zinc smelting plant is 4.5 to 5.2, which is basically within the optimum range of the test.

Fourth, the conclusion

(1) The cobalt removal agent AnBm is low in cost and is a commercially available ordinary commodity, and the raw material is easily available.

(2) The operating conditions are easy to control, and the removal efficiency of cobalt is higher than that of the zinc powder method. Under the optimal conditions (the amount of oxidant added is 42mg/L, the amount of decobalting agent is 2.4g/L, the reaction time is 50-60min; the temperature is 70-80°C, pH 4.1-5.0), and the cobalt removal efficiency is over 97%. The concentration of cobalt in the solution drops below 0.7 mg/L, which fully meets the requirements of zinc electrowinning.

(3) The production equipment is simple and can be produced by using existing equipment.

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