| The cement rotary kiln universally employs the magnesium chromium brick asliner of the tall temperate zone kiln. In high temperature, alkaline and oxidizing atmosphere, part of Cr3+ may be able to transform into Cr6"1", forming K.2CrO4 and so on, which is a severely toxic and carcinogenic chemical compound. The chromium public hazard problem obtains concern. Yet because of lacking scientific foundation, the laws limiting the use of magnesium chromium brick are not drawn up. And the forced steps of removing public hazards haven't been taken yet. In this dissertation the author analysed the magnesium chromium brick manufactured by 4000t/d's cement kiln of Tangshan Ji Dong cement plant thoroughly. The content of Cr6+ in themagnesium chromium brick disassembled from inner place of the kiln is ascertained.Also the total amount of Cr6+ discharged from the whole kiln is worked out. The author studied the stability of K.2CrO4 in natural state, assessed the pollution degree ofCr6+ in the deficient brick to the environment, and found detoxicating means. At the same time the correlative chemical reactions were analysed and discussed on thermodynamics.In the original, the deficient bricks were immersed with distilled water again and again, till the Cr6+ in them nearly dissolved. The total amount of Cr6+ discharged from the whole kiln was obtained, and then the pollution degree to theenvironment of the deficient brick of magnesium chromium discharged from the cement industry of our country was expected. The conclusion from the test is: The supreme Cr's content in the deficient brick of magnesium chromium may reach 2577 mg/kg. The largest permissible content of Cr6+ in portable water is 0.05mg/l. Also in other words: the deficient brick may polluteenvironmental water 50000 times the weight of itself.In this dissertation the author studied the chemical stability of K2CrO4 in the nature. Self decomposition is very hard to K2CrO4. Although KCrCU could be reduced by FeSO4 and MnSO4, it can not or is difficult to be reduced by NaaS or suchorganic matter as oxalic acid, citric acid, tartaric acid, grape sugar, acetaldehyde(40%)and ethyl alcohol(95%) and so on in the earth. Cr6+ discharged from the deficient brick of magnesium chromium will be in the nature and do harm to the health of human being and other living things over a long period of time.In the original the deficient bricks are detoxicated in the way of damp law and fire law separately. The damp law adopts FeSO4 as reductant and acquires better reduction effect. The proportion of FeSO4 ?7H2O to Cr6+ is from 30:1 to 50:1.After the reduction reaction, NaOH is added and adjusts PH's value to 8-9, and then deposits come into being. The defects of the damp law are as follows: The steps are multiple,and the discharged water, the concentration of S042" in which is high, is aptto pollute the environment again. The fire law utilizes the reducing atmosphere produced by sintered porous carbon stuff, and changes six prices chromium into lowprices substance. When the reducing temperature is 900 and the amount of carbon is 35%, the detoxicating effect is best. The fire law is easy to manipulate and won't pollute the environment again. So the fire law should be preferentially choosed. The conclusion from the theory analysis is that in the neighbouring alkalineenvironment of the deficient bricks, K2CrO4 is steady. In natural environment, the Cr + diffusing from the deficient bricks will decompose quite slowly. Six prices chromium was brought into being from high temperature oxidizing atmosphere;fit temperature and reducing atmosphere are needed when damaging it. Too low temperature isn't beneficial to reaction velocity and the formation of the gas in whichthe concentration of CO is high. When the temperature is too high , the maximum has9been reached to the concentration of CO. The oxygen pressure is getting higher with the temperature being cutted down. The reduction nature of the gas abates. Hence thereducing atmosphere is needed from the middle...
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