Discharge elimination of chromium metal and chromium salts production process of environmental pollution and waste obtained during utilization of it. Chromium is added to the iron ore of chromium soda ash, dolomite, limestone calcination temperature 1100 ~ 1200 â„ƒ, the residue was leached with water, sodium chromate. About 3 to 5 tons of chromium slag is produced per 1 t of chromate produced.
Ingredients The chemical composition of chromium residue is shown in the table below.
Chromium mainly composed of well-mineral periclase (MgO), dicalcium silicate (Î²-2CaO â€¢ SiO 2) , iron calcium aluminate (4CaO â€¢ Al 2 O 3 â€¢ Fe 2 O 3), calcium chromite ( Î±â€“Ca(CrO 2 ) 2 ), chrome spinel ((Mgâ€¢Fe)(CrO 2 ) 2 ), sodium chromate tetrahydrate (4Na 2 CrO 4 â€¢4H 2 O), and the like. Among them, a large part of the composition of the phase resembling cement, so the chromium slag is also hydraulic, and agglomerates in the air.
Hazard The main poison in the chromium residue is water-soluble sodium chromate tetrahydrate. Sodium chromate is a strong oxidant and is highly toxic. The chromium slag stack not only occupies the land, but also the fine particles fly with the wind to cause air pollution; the chromium slag is stacked in the open air and is immersed in rain and snow. The hexavalent chromium contained in the slag is dissolved and infiltrated into the groundwater or into the rivers and lakes, polluting the environment. The chromium slag yard of a certain iron alloy plant in China has not taken corresponding anti-seepage measures, causing the groundwater hexavalent chromium ion content to soar to 150-180mg/L, which is thousands of times higher than the drinking water standard, forming serious pollution pollution and downstream pollution. The scope has been increased to 15 to 20 km 2 . The domestic water consumption of several villages in the polluted areas depends on the introduction of tap water from outside or the supply of water by vehicles; various crops are also polluted to varying degrees. Aerosols of hexavalent chromium, chromium compounds and chromium compounds can harm human and animal health in many forms. Therefore, the storage yard of chromium slag must be paved with anti-seepage and additional hoods.
Handling and Utilization The way to prevent chromium slag contamination is to detoxify. Hexavalent chromium can be reduced under acidic conditions with a reducing agent, or under alkaline conditions with alkali metal sulfides or hydrosulfides, or at high temperatures and anoxic conditions in the presence of sulfur, carbon and carbide. It is a less toxic trivalent chromium. There are six main aspects of the use of chromium slag.
1. Making sintered bricks. The chromium slag is dried and pulverized, and the ingredients are mixed according to the ratio of 40% of chromium slag powder and 60% of clay , and are billed and baked. In high temperature and strong reducing environment, hexavalent chromium is reduced to trivalent chromium which is insoluble in water, eliminating highly toxic, and bricks can meet construction requirements.
2. Manufacturing cement. Using chromium slag, limestone, clay and other raw materials in accordance with ordinary Portland cement, cement clinker can be fired to make cement. The chromium residue after carbon reduction is the same as the blast furnace slag, the converter steel slag and the Portland cement clinker. Adding about 5% of gypsum can also produce less clinker steel slag cement.
3. Production of chromium slag cast stone. Mix 30% chromium slag, 25% silica sand (including SiO 2 >95%), 45% flue ash, 3% to 5% iron oxide scale (rolled steel skin), pulverize, and melt in a 1500 Â° C tank kiln at 1300 Â° C Under the casting, crystallization, annealing and slow cooling is the finished product, the simulated diabase stone composition is an excellent acid and corrosion resistant material.
4, the production of calcium and magnesium phosphate fertilizer instead of serpentine. The main components of serpentine are MgO and SiO 2 , which can be replaced by chromium slag. First pelletizing chromium slag, anthracite by: Phosphate: Chromium: silica = 37.5: 50:35:15 (weight ratio) is the ratio of ingredients was charged in a blast furnace, melt reaction at 1600 deg.] C, quenched by water quenching Cold, drain separation, drying in the drum, the ball mill smashed to get the finished product.
5. Replace dolomite and limestone for ironmaking flux. The content of CaO and MgO in the chromium slag is similar to that in the dolomite and limestone used in iron making, and can replace the dolomite and limestone iron making. Refining 1t pig iron consumes 600kg of chromium slag, hexavalent chromium can be completely reduced and detoxified thoroughly, and the chromium content of pig iron rises, hardness, wear resistance and corrosion resistance are improved.
6. Instead of chromite ore as a glass colorant. Chromium ore fines are commonly used as colorants in the manufacture of green glass, mainly by utilizing the optical properties of trivalent chromium ions in glass. The chromium slag contains a part of unreacted chrome ore and hexavalent chromium. The high temperature is favorable for the conversion of hexavalent chromium to trivalent chromium, completely detoxification, and the obtained product has bright green color. The chromium slag addition amount is preferably 3% to 5%.
In addition, the water-quenched chromium residue can also be used as a cement mixed material, a mineral wool raw material, a heat-resistant cementing material, a molten cement raw material, and the like. Since chromium slag is toxic and difficult to transport, its use is limited.
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