Industrial application of new technology for preparing metal zinc powder by alkali leaching-electrolysis

(Author: School of Urban Construction, University of South China; State Key Laboratory of Pollution Control and Resource Reuse, Tongji University; School of Nuclear Resources and Nuclear Fuel Engineering, Nanhua University)

Integrated treatment of waste containing zinc, zinc not only can improve the utilization of resources, reduce waste of resources, will also address the problem of environmental pollution smelting industry. Zhejiang Fuyang is one distribution center and secondary copper smelting base in China's large copper scrap. Meanwhile copper smelting produce significant amounts of copper are also reproduced, zinc, lead and other divalent metals with smoke. Zinc-containing soot with a zinc oxide mass fraction higher than 60% can directly produce zinc sulfate, zinc chloride and lithopone, while the content of zinc oxide with a mass fraction of less than 60% is complex and contains many other components, which cannot be used as a wet method. Zinc-smelting raw materials have not been well developed and utilized.

The zinc-containing waste is alkali leached and the leaching solution is electrolyzed to produce high-purity zinc powder. This technology has successfully built a zinc powder smelting plant in Guizhou and Yunnan. In 2007, Fuyang, Zhejiang Province built a 2000ta zinc powder production plant using copper fu ass as raw material. In the design of the plant, the advanced treatment process of waste electrolyte was added, and the equipment selection and structure selection of materials were improved, and the product quality control measures were further improved. Since the trial production in May 2007, a good production index has been achieved: the zinc leaching rate is greater than 90%, and the zinc powder quality has reached the national first-class standard.

First, the process principle and process

(1) Basic principles

In copper smelting soot, zinc is mainly present in the form of ZnO. Zinc oxide is soluble in sodium hydroxide solution, and metal elements such as copper and iron are hardly soluble and remain in the leaching residue. The main reactions of leaching are as follows:

(two) process

The process flow for alkali leaching of copper smelting soot and then electrolysis to produce metal zinc powder is shown in Figure 1, and the equipment connection diagram is shown in Figure 2.

Fig.1 Process for preparing metal zinc powder by alkali leaching-electrolysis method of copper smelting soot

1-leaching kettle; 2 filter press; 3-leaching slag; 4-purifying kettle; 5-purifying filter press;

6-purification slag; 7-aging pool; 8-electrolyzer; 9-electrolyte circulation tank;

10-zinc powder and waste electrolyte chute; 11-zinc powder cleaning filter tank;

12-zinc powder cleaning centrifuge; 13-zinc powder dryer; 14-waste electrolyte pool; 15-washing pool

Figure 2 Zhejiang Fuyang zinc powder smelting plant equipment connection diagram

Second, the design of zinc powder smelter

(1) Material calculation

The zinc powder smelter with an annual output of 2000t is calculated to be 6.2t of metal zinc powder per day. The daily preparation of electrolyte is 233 m 3 , the purification liquid is 235.4 m 3 and the leachate is 238 m 3 . According to the raw material zinc grade 40%, zinc leaching rate of 85%, the total recovery rate of 90%, the daily demand for raw materials 21 t.

(2) Leaching section

Intermittent leaching was used. 3 sets of mechanical stirring tanks with a volume of 4,000 mm × 4000 mm and a volume of 50 m 3 , 2 sets of work, 1 set for use. The leaching kettle body is a reinforced concrete structure with a conical bottom and carbon steel anticorrosive, and is equipped with a carbon steel spiral steam heating pipe. Set liquid level observation hole, long thermometer, thermometer casing and liquid level tick. It adopts propulsion mixing, with anti-corrosion mixer and electric motor, and the speed reducer drives stirring. The waste electrolyte feed pipe, the washing water feed pipe and the feed port are arranged on the upper part of the leaching kettle, and the movable cover is added on the top. 3 sets of pressure filtration leaching solution of XA100-1000UkB type chamber filter press are used, 2 of which work and 1 set of spare.

(3) Purification section

The lead ions such as lead, aluminum and arsenic in the leaching solution are removed by using 1 # , 2 # and 3 # separating agents. The purification tank has the same structure as the leaching tank, and the quantity is matched. Since the amount of purification slag is much less than the amount of leaching slag, a pressure-resistant, acid-resistant xMA50-1000U K B -type chamber filter press is used for pressure filtration.

(4) Electrolysis section

The anode plate is a stainless steel plate, a titanium alloy plate cathode plate, the plate size of 800mm 500mm ×. The anode and cathode plates are respectively provided with conductive copper strips of 840 mm and 1000 mm in length, 40 mm in width and 12 mm in thickness. There are 4 sets of electrolyzers in the electrolysis workshop, 10 in each group, for a total of 40. The size of the electrolytic cell was 1860 mm × 700 mm × 1260 mm. The bottom of the electrolytic cell is a cone and a zinc powder discharge port is provided. The cell body is made of reinforced concrete and lined with 10 mm rigid PVC sheet. PVC sheet has stable chemical properties, fire-retardant and flame-retardant, reliable insulation performance, smooth surface, smooth, non-absorbent, non-deformable and easy to process. Each group of electrolytic cells is provided with four electrolyte circulating cells, and a circulation pump is separately arranged. The size of the electrolyte circulation tank is 4000 mm × 2000 mm × 2200 mm. The current electrolysis workshop has a current intensity of 12 000 A and a total voltage of 120 V. The ZHS12000A/(100-200) V rectifier is used.

(5) Zinc powder cleaning and drying section

The metal zinc powder washing equipment started to be used is a plate and frame filter press, but the zinc powder at both ends of the filter press and the zinc powder pressed in the middle of the filter cake are not cleaned and the water consumption is large; afterwards, the SD type three-legged crane is used. The bag unloads the centrifuge, but the base of the centrifuge is light and easily vibrates due to uneven feeding. Therefore, the XR1200-N type overhead suspension manual discharge centrifuge is used in this design. After the cleaning is finished, stop the shaking filter bag, and after the zinc powder is loose, it is discharged from the bottom of the casing. A dryer is installed directly below the bottom of the casing, and the zinc powder is directly introduced into the dryer to quickly dry, thereby effectively reducing the oxidation of the zinc powder.

The zinc powder drying equipment began to use a large vacuum drying chamber, but the zinc powder could not be flipped during drying, and the heat was uneven, and the lower layer of zinc powder was difficult to dry, so that the drying speed could not keep up with the zinc powder cleaning speed. Afterwards, the SZG-1000 SZG double cone rotary vacuum dryer was used. The dryer body was in a vacuum state, and the tank body rotated to turn the zinc powder up and down, inside and outside, which accelerated the drying speed of the material.

(6) Waste electrolyte deep treatment section

After the waste electrolyte is circulated for 10 to 20 times, an advanced treatment is required to recover the alkali and enhance the purification. Pump the waste electrolyte into the standby leaching tank or purification tank, add alkali to stir until the alkali is completely dissolved, let stand, dissolve the solution, and then extract the lower floc from the bottom of the tank to another spare kettle, then wash it. The water is pumped into the tank and mixed to obtain a deep treatment liquid. The treatment liquid was stirred and heated to 70 ° C, lime was added for 0.5 h, and then filtered, caustic slag was discharged, and the causticized liquid was returned to the spent electrolyte pool for leaching.

3. Zinc powder quality control and production operation status

The control of the production quality of the zinc powder smelter is essential to ensure the quality of the zinc powder. The technical parameters of each production section are shown in Table 1. Track and analyze the production process, determine the materials to be added in the next process, and sample and analyze the zinc powder products to ensure product quality. Table 2 shows the items and sampling points that need to be monitored during the production process.

Table 1 Technical parameters of each section

Table 2 Analysis items and sampling points

Zhejiang Fuyang Zinc Powder Smelter started trial production in May 2007 and officially produced in July. See Table 3 for the production and operation of the first batch of raw materials and product quality. The zinc leaching rate is very high, reaching over 92%; the total zinc content of the produced metal zinc powder is above 98%, and the metal zinc mass fraction is above 94%, in line with the national first-class standard.

Table 3 Production operation of smelter

Fourth, the conclusion

Alkali dip-electrolysis production of metal zinc powder technology for the treatment of copper and zinc dust, has the advantages of simple process, high metal recovery rate, strong material adaptability, good product quality, environmental protection and comprehensive resource recovery. The successful application of this process has promoted the development of integrated recycling technologies for secondary resources containing zinc.

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