New Process for Preparation of Lead and Zinc Concentrate by Alkali Dipping-Precipitation Method

The traditional zinc concentrate and lead concentrate production method is flotation of lead-zinc sulfide ore. However, after years of mining, the lead-zinc ore has less and less reserves, and the lead and zinc grades are getting lower and lower. Zinc oxide minerals such as smithsonite, willemite, and heteropolar ore are also important resources of zinc. The composition is simple, but the ore structure is complex, the process of mineral recovery is complicated, the selection index is low, and the use of chemicals is difficult to achieve automation. Therefore, the development and utilization of zinc oxide ore is limited. The foreign country's selection index for zinc oxide ore is: zinc content in concentrate is 36% to 40%, recovery rate is 60% to 70%, up to 78%; China's zinc concentrate grade is average 35% to 38%, individually reaching 40%, the average recovery rate is 68%, up to 73%. The gradual depletion of zinc sulfide ore and the increasing demand for zinc have led to the rational development and comprehensive utilization of low-grade zinc oxide ore. For the poor zinc oxide ore, the zinc leaching-Na ₂ S precipitation process can be used to prepare zinc concentrate and lead concentrate. The process flow is simple, and the lead and zinc recovery rates are over 80%, which enables the development of poor zinc oxide ore. use.

First, the test materials

The test raw materials were taken from a zinc oxide ore in Yunnan. The chemical composition is shown in Table 1. The ore composition is complex and the zinc grade is low, which is a poor zinc oxide ore.

Table 1 Chemical composition of zinc oxide ore

Second, the test principle, method and process

(1) Basic principles

Leaching is a process in which NaOH solution dissolves zinc and lead in poor zinc oxide ore. The main reactions are as follows:

Zn0+2Na0H+H ₂ 0→Na ₂ Zn(OH) ₄ (1)

Pb0+2Na0H+H ₂ 0→Na ₂ Pb(OH) ₄ (2)

In zinc oxide ore, zinc and lead are often associated, so the separation of lead and zinc is the core of the recycling of zinc oxide ore resources. Both ZnS and PbS are poorly soluble. In neutral and weakly alkaline solutions, the difference between the two is small. After adding sodium sulfide, zinc and lead will precipitate simultaneously. In the previous research work, it was found that when the NaOH concentration reached 2.5-11 mol/L, as long as the ratio of the amount of Na ₂ S and Pb added was appropriate, Pb would preferentially precipitate with Zn, thereby achieving separation of lead and zinc. The ratio of the amount of Na ₂ S reacted with lead is 1.5 to 2.0, so the obtained sulfide of lead is not a simple PbS, and its possible reaction formula is:

xNa ₂ Pb(OH) ₄ +yNa ₂ S→nPbS _y ↓+bNa ₂ Pb(OH)mS _(4-m)/2 ↓+kPb(OH) ₂ ↓+pNaOH (3)

The ratio of the amount of Na ₂ S reacted with zinc is 0.6 to 0.7, and the product is more complicated. The possible reaction formula is:

xNa ₂ Zn(OH) ₄ +yNa ₂ S→nZnS _y ↓+bNa ₂ Zn(OH)mS _(4-m)/2 ↓+kZn (OH) ₂ ↓+pNaOH (4)

(2) Test methods

1. Lead and zinc NaOH leaching

Leaching process parameters: initial alkali mass concentration 240g / L, constant temperature 90 ° C, stirring Zh. The chemical composition of the leachate and the leaching rate of each element are shown in Table 2. Be seen, the leaching rate of zinc and lead of more than 85%, Cu, Fe, Ni , Mg, Ca, Al and other metal elements are very low leaching rates, concentrations are less than 50mg / L, ensure lead, zinc fine The quality of the mine.

Table 2 Chemical composition of leaching solution and leaching rate of each element

2. Determination of process parameters of lead precipitation

Take 200 mL of the leachate in a 300 mL beaker, add a certain mass of Na ₂ S solid, cover the watch glass, and stir on a magnetic stirrer. After the reaction, the beaker was taken out and the supernatant was taken. The concentration of lead was analyzed by ICP method. The effects of Na ₂ S addition amount, temperature, reaction time and alkali concentration on lead precipitation were investigated.

3. Determination of process parameters of zinc precipitation

Take 200mL of lead-lead solution (ρ(Zn) = 28.80g/L, ρ(NaOH)=199.26g/L) in a 300mL beaker, add a certain amount of Na ₂ S solid, cover the surface dish, on the magnetic stirrer Stir at a constant temperature of 90 °C. After the reaction, the beaker was taken out and the supernatant was taken. The concentration of zinc and alkali was determined by EDTA complexometric titration combined with acid-base titration. The effects of Na ₂ S addition and reaction time on the zinc precipitation were investigated.

(3) Test process

The zinc concentrate and lead concentrate were prepared by NaOH leaching-precipitation process. The process flow is shown in Figure 1.

Third, test results and analysis

(1) Precipitation of lead

According to the test methods and conditions, the lead precipitation test results are shown in Figures 2 to 5.

As can be seen from Fig. 2, when the mass ratio of sodium sulfide to lead is about 1.8, the lead mass concentration is stable between 6 and 8 mg/L, so the optimum ratio of the quality of sodium sulfide to lead is determined to be 1.8.

It can be seen from Fig. 3 that the temperature rise is favorable for lead precipitation, and after 70 °C, the lead concentration in the leachate drops below 5.96 mg/L. Therefore, the optimum lead precipitation temperature was determined to be 70 °C.

It can be seen from Fig. 4 that the reaction time has little effect on lead precipitation, and it is preferable to consider the optimum reaction time for 0.5 h.

As can be seen from Fig. 5, the alkali concentration has no significant effect on the lead precipitation rate. Therefore, it is possible to directly precipitate lead after the alkali leaching without adjusting the alkali concentration.

(2) Precipitation of zinc

According to the test methods and conditions, the zinc precipitation test results are shown in Figures 6-7.

If the zinc-immersed liquid still contains S ^2- ions, S ^2- will precipitate with the dissolved zinc when the solution is recycled to the leaching stage, which seriously affects the zinc leaching rate. To prevent this from happening, 4 to 5 g/L of zinc is required in the solution. It can be seen from Fig. 6 that when the mass ratio of sodium sulfide to zinc is 2.4, the remaining zinc mass concentration is 5.19 g/L; when the ratio is 2.8, the remaining zinc mass concentration is 2.75 g/L, which is lower than 4 g/L. . Taken together, the optimum ratio of the quality of sodium sulfide to zinc is determined to be 2.4.

It can be seen from Fig. 7 that the reaction time has no significant effect on the zinc precipitation, but the reaction time has an obvious effect on the regeneration of the alkali, and the optimum reaction time is determined to be 3 h. At the time of leaching, the initial alkali concentration is 240g/L, and both the lead and the zinc deposits have alkali formation. After the zinc is dissolved, the alkali concentration of the solution can reach 244g/L. The alkali regenerated in the sedimentation section can compensate the alkali consumed in the leaching section. The entire process theoretical alkali consumption is zero.

(3) Quality of lead concentrate and zinc concentrate

The chemical compositions of lead concentrate and zinc concentrate prepared according to the above parameters are shown in Table 3. The quality of lead concentrate is far superior to the first-class standard of the industry standard YS/T319-1997, and the zinc concentrate reaches the third-level standard of the industry standard YS/T320-1997.

Table 3 Quality of lead concentrate and zinc concentrate and industry standard%

Fourth, expand the test and industrial design

Take the small-scale integrated zinc oxide mine of a mine in Guizhou for a small comprehensive process test of 1.2kg scale. The test conditions and results are shown in Table 4. It can be seen that the loss of zinc and lead mainly occurs in the process of leaching and solid-liquid separation, and the consumption of alkali is mainly the volatilization of the solution during heating, mainly the loss of liquid and the entrainment of concentrate during solid-liquid separation. The test uses natural filtration of Filter cloth, the solution loss is large, and the amount of alkali entrainment is large, which seriously affects the lead and zinc recovery rate and alkali consumption. In industrial production, the solid-liquid separation can be carried out by a filter press or a centrifuge, and the lead and zinc recovery rates can be further improved.

Table 4 % of small comprehensive test indicators

The process of preparing zinc concentrate and lead concentrate by alkaline zinc leaching-precipitation method can be industrialized and promoted, and a concentrating plant with an annual output of 2000-5 000 tons of concentrate can be built.

V. Conclusion

The alkali leaching-precipitation method can be used to prepare zinc concentrate and lead concentrate from the poor zinc oxide ore, and the process parameters of lead and zinc precipitation are determined. The lead-lead process conditions are as follows: the amount of sodium sulfide precipitant added is 1.8 times the mass of lead in the leachate, the temperature is 70 ° C, and the reaction time is 30 min; the zinc-zinc process condition is: the amount of sodium sulfide precipitant added is 2.4 times the mass of the precipitated zinc. The temperature was 90 ° C and the reaction time was 3 h. Under the optimal conditions, a small comprehensive test was carried out, and the zinc concentrate content of the zinc concentrate was 52%, the lead concentrate of the lead concentrate was 78%, and the recovery rates of lead and zinc were both above 80%. The process is simple, no external pollution, high recovery rate of lead and zinc, and can be industrialized and promoted.

Magnetic Pump

Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. They are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from which it exits.