China Education Equipment Purchasing Network News: Chromium slag is an industrial waste slag produced during the production of metal chromium and chromium salts, which has a certain degree of harm to humans. More than 20 provinces and cities in China currently emit chromium slag. ingredient The chemical composition of chromium slag is: silicon dioxide accounts for 4-30%, aluminum oxide accounts for 5-10%, calcium oxide accounts for 26-44%, magnesium oxide accounts for 8-36%, and iron oxide accounts for 2-11 %, Chromium hexaoxide (Cr2O6) accounts for 0.6 to 0.8%, sodium dichromate (Na2Cr2O7) accounts for about 1%, etc. The main minerals contained in the chromium slag are magnesite (MgO), calcium silicate (2CaO · SiO2), Brinell (4CaO · Al2O3 · Fe2O3) and 1-10% residual chromite. harm In the absence of reducing agents, the aqueous solution of sodium dichromate contains highly toxic hexavalent chromium ions. The chromium slag is piled up in the open air and is immersed in rain and snow. The hexavalent chromium contained is dissolved into the groundwater or into rivers and lakes, polluting the environment. The content of hexavalent chromium in the water in the heavily polluted zone can be as high as tens of milligrams per liter, which is several times higher than the drinking water standard. Hexavalent chromium, chromium compounds and chromium compound aerosols can harm human and animal health in various forms. Therefore, the storage site of chromium slag must be paved to prevent seepage and additional shed covers. Pollution incident Chromium pollution incidents are not uncommon in the world, especially in the 1970s, Japan and the United States have experienced serious chromium pollution incidents. In 1993, the chromium pollution case in California, USA caused a sensation and was moved to the screen. The film titled "Never Compromise". The film describes a female lawyer who accidentally discovered that the largest hydroelectric gas company in the United States illegally discharged toxic sewage containing hexavalent chromium. She believes that this may be the root cause of the deadly disease suffered by local residents. She uses unimaginable willpower for local residents. Won huge compensation of USD 333 million. In fact, the plot in the movie is not far from us. Just around our city, the huge heap of “ownerless†chromium residue left behind by some companies has been quietly hidden for decades. In the 1980s and 1990s, the international community generally recognized the harm of chromium slag. The Chinese government began to attach importance to the control of chromium slag pollution, comprehensively rectified the chromium salt industry, and gradually shut down and transferred more than 40 chromium salt enterprises. The enterprise closed, but a large number of "unowned" chromium residue piles were left. In more than 20 cities including Shanghai, Tianjin, Suzhou, Jinzhou, Baotou, Wuhan, Qingdao, Hangzhou, Shenyang, Jiangmen, Changsha, Guangzhou, Shaoguan and Zhengzhou, more than 6 million tons of chromium slag have been left. Due to technical and financial constraints, there was no ability to harmlessly treat these chromium slags, so chromium slag "fortresses" were formed. According to a document from the Ministry of Environmental Protection, almost all the companies that produce chromium slag were built in densely populated areas, scenic areas, and upstream areas of water sources. Only a few enterprises have anti-leakage facilities for the chromium slag piles produced, and most of the rest are simply piled up. After being continuously washed by rainwater, the hexavalent chromium in the chromium slag flows into nearby surface water or seeps into groundwater, causing serious pollution to surface water, groundwater and soil. Handling and utilization The method to prevent the harm of chromium slag is to carry out high temperature treatment to eliminate its toxicity. Hexavalent chromium can be reduced under acidic conditions with reducing agents, or under alkaline conditions with alkali metal sulfides and hydrosulfides, or under high temperature and anoxic conditions with sulfur, carbon and carbides It is trivalent chromium with low toxicity. The use of chromium slag mainly has the following aspects: ①Making sintered bricks: drying and crushing chromium slag, mixing the ingredients according to the proportion of chromium slag powder 40% and clay 60%, making bricks, and firing them in kiln. In high temperature and strong reducing environments, hexavalent chromium is reduced to water-insoluble chromium trioxide, eliminating highly toxic. Bricks can meet construction requirements. ② Making high-strength chromium-barium brick: mix 5 parts of chromium slag and 3 parts of barium carbonate slag, add 40% water, and wet grind in the ball mill. The hexavalent chromium in the chromium slag becomes barium chromate insoluble in water, and part of it is converted into trivalent chromium. According to 3 parts of chromium barium slag slurry and 2 parts of coal slag ingredients, after rolling and simmering, make bricks. Then, after heating, constant temperature and cooling for 2 hours each, autoclave curing is carried out under 8 atmospheric pressures to make chromium barium bricks. The chromium slag contains more magnesium oxide, the volume will expand, it needs to be stored for a period of time, and the volume is stable before use. ③ Chromium slag casting stone: with 30% chromium slag, 25% silicate and 45% coal slag ingredients, and then mixed with 3 to 5% iron oxide, after melt casting, crystallization annealing, the compressive strength is 4800 to 5500 Kilogram-force / cm high-strength, wear-resistant, corrosion-resistant cast stone. ④Cement making: using chromium slag, limestone, clay and other raw materials according to ordinary Portland cement ingredients, it can burn cement clinker to make cement. Using carbon-reduced chromium slag, together with blast furnace granulated slag, converter steel slag and portland cement clinker, adding about 5% gypsum can also produce less clinker steel slag cement. In addition, chromium slag can also replace chromium ore powder as an emerald green colorant for glass. Water quenched chromium slag can also be used as cement mixed materials, mineral wool raw materials, heat-resistant gelling materials, molten cement raw materials, etc. Japan adds ferrous sulfate, ferrous oxide and other reducing agents to the chromium slag after detoxification to make plastic solidified materials or as gypsum board filler. Chromium slag is toxic and difficult to transport, and its use has not yet opened up. Made of supreme quality EVA material, water resistant, moisture proofing and dust-proof. Watch Travel Case ,Custom Watch Case,Eva Watch Case,Eva Hard Watch Case Shenzhen Guohui Craft Products Co.,Ltd. , https://www.evacarrycase.com
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Chromium slag is toxic, how should we use it?