| China owns the largest caustic soda production capacity and consumption in the world, resulting in the large production of caustic soda chemical waste in the systems, such as salt mud, waste inorganic membrane, waste sulfuric acid and so on. They are difficult to deal with, piling up over many years, restricting the development of caustic soda industry seriously. In this study, we carried by site investigation, samples analysis and risk assessment of caustic waste, to reasch the generation characteristics and pollution characteristics of caustic soda industry waste, and then gave some advice on the risk of waste contamination control.Site investigation showed, diaphragm process making caustic soda mainly generated sault mud, waste separator, mirabilite and waste sulfuric acid. By this process, when per ton of caustic soda produced, consumption of raw salt was 1462.5 kg, generation of salt mud was 62.5 kg, and the waste diaphragm was approximately 0.13 kg, waste sulfuric acid was about 26.1 kg, mirabilite was about 25.5 kg. Lonic membrane process making caustic soda mainly generated sault mud, waste sulfuric acid and mirabilite. By this process, when per ton of caustic soda produced, the consumption of raw salt was 1462.5 kg, and the generation of salt mud was 93.3 kg, waste sulfuric acid was about 26.1 kg, mirabilite was about 25.5 kg.By the results of the experiment analysis, we can find that the major component of salt mud were CaCO340%?97%, NaCl 3%?16%, SiO27%?10%, and it can also find BaSO430% used denitration technologies. The contents of chromium, zinc, barium, mercury, copper, cadmium, lead and some other heavy metals does not exceed the standard of "soil environmental quality standards". The pH of salt mud was between 11 to 12. The leaching toxicity of the above heavy metals were lower than hazardous waste identification standard, so salt mud does not have the characteristics of hazardous waste. The experimental analysis found the main type of waste separator samples were chrysotile which was a kind hazardous waste. The concentration of waste sulfuric acid was about 75%, it did not contain heavy metals, but the content of chloride was about 0.04%. Seventy percent composition of mirabilite is Na2SO4, followed by NaCl, where the content of main heavy metals had almost no excessive phenomenon compared to "soil environmental quality standards".The solid residue of heavy metals caused by dissipation and leaching will harm the environment and human health, the research selected RBCA model to do risk characterization and then got the risk of salt mud stockpiling acceptable. The way of salt mud recycling is still on trial, such as making construction materials and desulfurizert, there are many problems in these ways, so it is difficult to promote in the enterprise. So the main treatment of the waste is landfill nearby the caustic soda industry currently. First of all, the salt mud control should actively pursue reduction measures to reduce its production capacity, then take more researches on its recycling technology, and promote the relevant demonstration projects actively. Membrane waste contains hazardous waste, they are depth landfill by cement solidification currently. As the diaphragm caustic soda production capacity devices have been eliminated, diaphragm waste will be completely resolved then. The waste sulfuric acid is absence of impurities, its recycling and reuse is an inevitable choice, enrichment technology and recycling and other technologies can effectively solve the problem of waste sulfuric acid, it is worth promoting. Waste sulfuric acid is managed as hazardous waste now, there are a lot of difficulties, in the efforts of the industries and the administration, comprehensive utilization rate of waste sulfuric acid will be improved, it is expected to be a byproduct of caustic soda industry. |
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