I. Introduction

Electrolytic manganese metal is a very important chemical raw material, widely used in iron and steel, nonferrous metals, chemicals, pharmaceuticals, food and scientific research. China built its first production line in 1956. In 2004, the output of electrolytic manganese in China reached 494,000 tons, making it the world's largest producer, exporter and consumer of electrolytic manganese.

Clean production refers to the goal of “energy saving, consumption reduction, pollution reduction and efficiency improvement” through continuous improvement of design, adoption of advanced technology and equipment, use of clean energy and raw materials, improvement of management, and comprehensive utilization. Clean production is the only way to realize the environmental protection strategy from the "end" control to the whole process of pollution control. It is also an important way to implement the scientific development concept and guide enterprises to take a new road to industrialization. As a highly polluting and energy-intensive industry, electrolytic manganese is particularly important for clean production.

This paper takes the production process of the domestic electrolytic manganese leading enterprise CITIC Dameng Mining Co., Ltd. Daxin Branch as an example to analyze the clean production of electrolytic manganese industry.

Second, research examples

The main raw materials of the company's electrolytic manganese are manganese carbonate powder, concentrated sulfuric acid, manganese dioxide powder and liquid ammonia, and the auxiliary additives are sodium fumarate and selenium dioxide. Through the continuous research and improvement of electrolytic manganese technology, the current process is shown in Figure 1.

Process description: The electrolytic cell anolyte and 98% concentrated sulfuric acid are sequentially introduced into the chemical mixing tank, and the manganese carbonate powder is added by the feeding vehicle. When the reaction is near the end point (by the residual sulfuric acid detection indication, 8-9g∕L), manganese oxide is added. Prepared by reduction and calcination of manganese dioxide), when the reaction is near the end point (2~3g∕L of residual acid), manganese dioxide (anode mud) is added to oxidize low-cost iron, and liquid ammonia is added to adjust the pH to 3.8-4.2 to make iron as Fe ( The form of OH) ₃ is precipitated, and the above steps are all carried out in a compounding tank. The leachate is then sent to a filter press plant where it is pressure filtered through a plate and frame filter press and the filtrate enters the settling tank. Sodium fumarate (C ₃ H ₆ NS ₂ Na·2H ₂ O) was added to precipitate a heavy metal such as Co or Ni in the filtrate as a chelate, and the test paper was tested for no heavy metal, and then the fine filtrate was obtained by plate-plate pressure filtration. The temperature of the concentrate filtrate is generally around 80 ° C, and the suitable temperature for electrolysis is between 38 ° C and 42 ° C. It needs to be cooled. Naturally cool in the static pool, manganese is easily oxidized during electrolysis. It is necessary to add 2 to 3 kg/t of selenium dioxide as an antioxidant in the static storage tank. The static adjustment process is generally 24 hours, and a qualified electrolyte is obtained. . Then, the qualified liquid is sent to the electrolysis cell for electrolysis, and the manganese plate of the purity of 99.9% is precipitated in the cathode plate of the electrolytic cell, and the product is obtained after passivation, washing, drying and stripping. The electrolytic cell is separated from the anolyte by a separator bag, and the anolyte contains a large amount of Mn, (NH ₄ ) ₂ SO ₄ and H ₂ SO ₄ , and is reused in the leaching step. The anode produces anode slime (more than 90% is MnO ₂ ) and is reused in the oxidation and iron removal process.

Figure 1 Flow chart of electrolytic manganese production process

Third, clean production analysis

(1) Process analysis

1. Neutralization

According to the process requirements, the residual acid of the leachate must be controlled at 1~2g/L. At the end of the leaching of manganese carbonate, the residual acid is 8-9g/L, so it needs to be neutralized. Traditionally, the double fly powder (the main component is calcium carbonate) is neutralized, a large amount of acid is wasted, and the amount of slag is increased, which increases the pressure filtration. burden. The company found that the use of manganese monoxide neutralization, the reaction end acid is only 2 ~ 3g / L, can replace the double fly powder, reduce the use of liquid ammonia, but also increase the manganese content of the leachate. According to estimates, after neutralization with manganese monoxide, each tank (about 140m ³ ) can reduce the filter residue by 1.1t and save liquid ammonia by 0.4t.

2, anolyte, anode mud reuse

The anolyte contains a large amount of H ₂ SO ₄ , (NH ₄ ) ₂ SO ₄ and Mn ²⁺ , and the main component contents thereof are shown in Table 1.

Table 1 Main component content in anolyte

The anolyte is about 45m ³ per ton of metal manganese. The leaching process can save 1.7t of sulfuric acid, 4.7t of ammonium sulfate and 0.4t of Mn ²⁺ . MnO ₂ accounts for more than 90% of the anode mud, and reuses the oxidation and iron removal process to save about 100 tons of MnO ₂ powder per month.

(II) Analysis of main equipment and raw materials

1, roasting equipment

Reducing the calcined manganese dioxide is a manganese oxide, a conventional reflective reduction roasting oven at 800 deg.] C high temperature, long reaction times, coal energy to generate air pollutants, while the high temperature conditions of workers body adversely. Studies have shown that manganese has microwave absorption characteristics. The microwave roasting equipment that has been developed at present has electricity as energy source, can be continuously fed and mechanized, and is a clean and advanced manganese ore roasting process. The main economic and technical parameters of the reverberatory furnace roasting and microwave roasting are shown in Table 2.

Table 2 Comparison of economic technical parameters between microwave roasting and reverberatory furnace roasting

It can be seen that microwave roasting is superior to conventional reverberatory furnace roasting in terms of energy cleanliness, pollution generation, efficiency and operation mode, which is in line with the principle of “decreasing pollution and increasing efficiency” in clean production.

2, raw materials

In the stage of vulcanization and heavy metal addition, sodium fulme is added. The reaction of sodium sulphide with heavy metals is a chelation reaction, which solves the problem of generating H ₂ S gas when traditional sulfides are used, and protects the health of the population.

The amount of selenium dioxide added to the electrolyte is about 2 to 3 kg/t. Selenium dioxide is a kind of drug, which has strong irritating effect on skin and mucous membranes. A large amount of inhalation of its vapor can cause chemical bronchitis, chemical pneumonia and pulmonary edema. At the same time, it is expensive, and the market price has reached 600,000 in recent years. Yuan / t. Sulfur dioxide can also exert the same antioxidant effect. Because sulfur dioxide is in a gaseous state, the company currently uses the method of adding (NH ₄ ) ₂ SO ₃ in the stationary tank to increase the sulfur dioxide content in the electrolyte and reduce some of the selenium dioxide. Joined.

(3) Three waste treatment

1. Comprehensive utilization of filter residue

The pressure filtration includes initial pressure filtration and fine pressure filtration. Both of them adopt the plate basket pressure filtration. The finished manganese solution is about 5 to 6 tons, and the primary filtration residue accounts for more than 90%. The company's electrolytic manganese production is about 30,000 t / a, and the amount of filter residue is about 15 to 180,000 t / a. The filter residue piles up a large amount of land, contains a large amount of Mn, Fe and a variety of heavy metals, and the filter residue has a very fine particle size, which easily enters the water and soil environment and causes environmental pollution. At present, many manufacturers have problems in the treatment of filter residue, which is more serious to the local environment.

(1) Multi-element analysis of filter residue, see Table 3.

Table 3 Content of each component in the filter residue

(2) Comprehensive utilization of filter residue

The comprehensive utilization of primary filtration slag has been studied for a long time. The main idea is to recover manganese minerals first, then make bricks as tailings or as road landfills. The recycled process wastewater is recycled after treatment. The separation is realized by the large difference of the magnetization coefficient of manganese minerals and other minerals. It is found by X-ray diffraction analysis and high-power microscope that the surface of the manganese mineral is covered by the acid leaching process, and the plaster of the surface layer must be destroyed. Magnetic separation effect. After many tests, it was found that pre-grinding to 120 mesh accounted for more than 90%, and then strong magnetic rough selection, the final strong magnetic sweeping effect is better, manganese mineral recovery rate can reach more than 60%. The total tail sludge after recovery of manganese minerals still accounts for more than 80%, mainly containing SiO ₂ , CaO, Fe ₂ O ₃ and the like. The plasticity index is 11.6, and the uniform consistency moisture content is 18%, which is in line with the conditions for making brick materials for civil use. The hardness of the brick can be modified by adding clay. The ratio of the tail mud to the clay is 7:3, and the temperature is 100 ° C for 4 h, and the obtained brick can reach the national second-class civil brick standard.

The company independently studied the recycling of slag. Co and Ni in the sulfurized slag are (C ₃ H ₆ NS ₂ ) ₂ Co, (C ₃ H ₆ NS ₂ ) ₂ Ni chelate, and the [C ₃ H ₆ NS ₂ ^- ] group has good hydrophobicity. In the case of no flotation agent, it can be enriched by flotation. The equipment is used as a flotation column, and the recovery step is: after the flocculation slag is floated and concentrated by flotation column, the concentrate is dechlorinated by acid leaching, goethite method, 10% P204-kerosene solution decontamination, quaternary ammonium chloride 7401 Extraction and separation of cobalt nickel , carbonate precipitation of cobalt, nickel, to obtain product cobalt carbonate and nickel carbonate. Under the current process, the recovery rate of precious metals is over 70%.

2, water reuse

Each ton of electrolytic manganese finished product produces about 350m ^{3 of} process wastewater, mainly referring to passivation wastewater and washing wastewater. The passivation is a waste plate, using the weight generated when the potassium silicate solution of chromium passivation products; including washing wastewater washer, wash cloth, wash block, clear the groove, the ground flushing. The passivation wastewater of the plant is about 0.5m ³ /d. The passivation wastewater has high heavy metal content and high toxicity, and is treated as a dangerous solid waste commissioning unit.

The 1t metal manganese product produces about 300-330m ^{3 of} washing wastewater, which is characterized by low pH, generally around 4.5; wastewater contains harmful components such as Cr ⁶⁺ , Mn ²⁺ and NH ₃ -N, but the content is not high. It has more suspended solids and large chroma, which is a serious hazard to human health and crop growth.

At present, the washing wastewater treatment technologies mainly include:

Flocculation precipitation method: adjust the pH value to make Mn form Mn(OH) ₂ colloid. The lower the zeta potential of the colloid is, the more unstable it is. The addition of flocculant can reduce the zeta potential of the colloid and achieve the effect of rapid destabilization. Yao Jun uses a polymerized chloride or the like as a flocculant. When the pH is 9.5 and the optimum dosage of the polymerized chloride is 35 mg/L, the Mn removal rate reaches 99.76%. Fan Yuchuan et al. studied lime-basic aluminum chloride. As a flocculant, in the experiment, the pH value was 8.5 to 10, and the optimum basic aluminum chloride dosage was 50 mg/L, and the Mn decreased from 397 mg/L to 0.2 mg/L.

Iron filings micro-electrolysis: After adding iron filings and inert carbon particles to the wastewater, the wastewater can be modified to form a primary battery. After energization, H+ is continuously consumed, so that the OH ^- concentration is increased and the metal ions are removed as hydroxides. Ouyang Yuzhu et al. showed that the removal rate of Cr ⁶⁺ and Mn ²⁺ can reach over 99.7% under the condition of 15% iron filings, pH value of wastewater 4.0 and reaction time of 120 minutes. The total chromium removal rate is up to 99.7%. 99.2%.

The liquid membrane separation method and the emulsion membrane separation technology are a new, efficient, rapid and energy-saving separation technology, which has the advantages of simple process equipment, high separation speed and high selectivity. When the heavy metal ion-containing wastewater is in contact with the emulsion, the metal ion transfer process is mainly divided into two steps, and the reaction equation is:

Extraction reaction: M+B→[MB]

Back extraction reaction: [MB]+A→MA+B

According to the mass transfer principle, the metal ions in the wastewater are concentrated in the inner phase of the membrane through the liquid membrane, thereby achieving the purpose of separation. The flocculation precipitation method and the iron filing micro-electrolysis method have many researches on the treatment of electrolytic manganese industrial wastewater, and the technology is relatively mature, and has been applied in industry. There are few studies on the treatment of electrolytic manganese industrial wastewater by liquid membrane method, but the liquid membrane treatment of industrial wastewater can achieve the dual functions of resource recovery and environmental protection. It has the characteristics of low investment and high efficiency. It is a clean technology with broad application. prospect.

The company's location is a water-deficient zone, and reclaimed water is an important source of water. Combined with the characteristics of current flocculation and sedimentation and iron filings electrolysis, the company now adopts the “iron-carbon microelectrolysis bed to reduce hexavalent chromium + soda lime emulsion flocculation + blast deamination treatment process”, the process flow chart is shown in Figure 2.

Figure 2 Sewage treatment process flow chart

After the treatment of the process, the removal rate of Mn and Cr reaches 95% or more, and the requirement for reuse can be achieved. However, there are still many gaps in the recovery of mineral resources relative to the liquid membrane separation method.

3. Exhaust gas prevention

Exhaust gas is mainly produced in the leaching and electrolysis stages.

When leaching, the reaction is severe, and it is easy to produce sulfuric acid mist. The workshop should be built in the downwind direction of the plant, using negative pressure to draw air, sodium carbonate solution to absorb, and organized high-altitude discharge to eliminate pollution. When manganese powder is put into feeding, it is difficult to uniformly feed the traditionally used crane bucket to feed, and it is easy to cause dust to fly. The company uses feeding vehicles to solve the problem of uniform feeding and dusting.

The electrolysis temperature is between 38 ° C and 42 ° C, and ammonia gas is easily volatilized. Because it is unorganized emission, and the points are wide and wide, it is not easy to control. Generally, the open workshop design is adopted, the skylight is opened on the roof, and the concentration of ammonia gas is reduced by forced ventilation. The workshop workers wear caps and wear masks to avoid injury.

4. Suggestions and measures for cleaner production

(1) Cleanliness of raw and auxiliary materials

From the source control, priority is given to non-toxic, low-toxic, less polluting raw and auxiliary materials to prevent the harm of raw materials and products to humans and the environment. (1) Neutralization of residual acid with manganese monoxide reduces the amount of liquid ammonia used; (2) Selenium dioxide is a highly toxic substance, and ammonium sulfite is used to reduce the amount of selenium dioxide added.

(2) Cleanliness of process equipment

It adopts new processes and equipments with high conversion utilization rate, low emission coefficient, energy saving and consumption, and is conducive to automation of production operation control, achieving the purpose of energy saving, consumption reduction and pollution reduction. Through the analysis of the previous cleaning production equipment, it is recommended that the company install the microwave roasting equipment as soon as possible; the manual removal of the board method makes it easy to bring out the electrolyte and cut the diaphragm bag. It is recommended to use a crane to remove the board and mechanize the operation.

(3) Prevention and treatment of pollution

For the comprehensive utilization of tailings, it is recommended that it continue to invest in research funds to further improve the recovery efficiency; at the same time, the management of slag stacking should be properly solved to avoid secondary pollution; the reuse of water to the leaching process can save Mn process; leaching, Green belts should be built around the workshops such as electrolysis to reduce pollution to the surrounding environment.

(4) Control and management of the production process

Electrolytic manganese production, the degree of dependence on people is relatively high, the implementation of the post and target responsibility system, especially the standardization operation to remove the board, to prevent the removal of electrolyte, washing, scouring, etc. to pay attention to water conservation, so that artificial resource waste and pollution Minimize emissions; the special nature of continuous electrolysis, it is recommended to take measures to prevent power outages, establish an emergency power generation system in the factory, regularly check circuits, update aging lines, strengthen equipment management, and improve equipment integrity and operation rate.

V. Conclusion

As a high material consumption, high energy consumption and high pollution industry, electrolytic manganese promotes clean production in enterprises, and improves the electrolytic manganese industry by adopting clean raw and auxiliary materials, advanced process equipment, waste residue recovery and reuse of water. The environmental and economic benefits have important practical significance and are the only way for the sustainable development of China's electrolytic manganese industry.

Tset

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