Study Of Bacterial Detoxification Of Chromium Slag Process

Along with the rapid growth of the national economy, chromium compound in our country is developed rapid. At present, the production and consumption of chromium compound in our country is the highest inthe world. But the poisonous waste residue -chromium-containingslag which is discharged during the production of chromium compound is toxic . It contaminated the environment seriously and harm to the human health . Every year, about 600,000 tons chromium-containing slag is discharged in our country. The accumulative total of the last is 6,000,000 ton, but the quality which is deal with detoxification and comprehensive utilization is less than 17%. There are 12,500,000 tons soil is contaminated severely. Now the main processing method of the chromium-containing slag are all have the problem of high cost, low disposal amount and secondary pollution.The biological method deal with the chromium-containing waste water is attentioned broadly and developed rapidly in recent years due to the low investment and low function fees. But the report of the biological treatment of chromium-containing slag is scarcely.In the face of the research state, our research group obtained effective bacteria named Ch-1 which is isolated from sludge nearby the chromium slag site through several years work. The bacteria Ch -1 is suited to alkaline condition and the tolerance ability can reach pH=12 , the Cr( VI) tolerance concentration is above 4 g/L. At the same time, the Cr (VI) can be detoxificated under the high pH and high Cr (VI) concentration.On the basis of research, the new way to chromium-containing slag detoxification by microbe is coming into being: feasibility study is conducted through bottle experiment; then optimize the technical condition by column experiment; finally technical grade experiment is conducted.On the basis of above research, the innovative conclusions were obtained as follows. 1. The Cr(VI) content in the chromium-containing slag is 7.394 g/kg , the water-solubility Cr(VI) content is 1.756 g/kg ,and the leaching toxicity is 22.133ppm which is all far beyond the national level. However, the problem of the leaching water can be solved out when the bio-detoxification is conducted. During the detoxification period, the pH of the leaching water can be reduced to 8-9 and the Cr(VI) concentration reduced to 0ppm.2. The result of the column experiment showed: temperature partical size and initial pH are important technical impact factor. The preferable result can be obtained when the temperature is 28℃, the partical size is in the scale of 4mm to 8mm and the initial pH value is 10.0. The Cr(VI) content is reduced from initial 7.394 mg/kg to 0.585mg/kg in the end,the leaching percent is 92.088%.3. The pilot plant research verified the bio-detoxification of the chromium-containing slag is feasible in industrialization. It is a innovate way to the detoxification of the chromium-containing slag. Condition optimization experiments is conducted by "granulating-bacterial heap leaching". The demonstration project of 10 tons/ batch is functioned and the result demonstrate that the chromium containing slag is detoxification completely after 7-10 bio-leaching and reached the leaching toxicity discriminate national standard of hazardous waste (GB5085-1996) .The treatment cost for every ton chromium containing slag is 200 yuan.