| Polyvinyl chloride(PVC)is an important kind of organic polymers,and it has many applications in chemical industry,electric power industry,construction industry and so on.At present,calcium carbide method is the most mature technology for the production of acetylene,which is the raw material of PVC,but the control of environmental pollution is lagging behind in this process.The waste sulfuric acid produced from the purification of acetylene is very difficult to deal with for its complex compositions.How to harmless treatment,reduction and resource utilization of the waste sulfuric acid is a key factor that influences the clean production of PVC.In this paper,the waste sulfuric acid produced from a chemical company in northern Shaanxi province was selected as an test subject,and the main factors that result in poor quality of the gypsum produced by waste sulfuric acid was discussed.A feasible process of waste sulfuric acid treatment and its resource utilization for the production of gypsum is proposed.The main contents and results are shown as follows:(1)Physical properties of the waste sulfuric acid were analyzed,and also the solid and liquid impurities were analyzed by elemental analysis.It was found that the solid insoluble matter and the organic matter were the main factors that result in poor quality of the gypsum produced from waste sulfuric acid.The waste sulfuric acid was treated by filtering and heating,and the key factors that influence the quality of waste sulfuric acid were discussed.The acidity of the waste sulfuric acid increased 25.0%,the content of solid suspended matter decreased 95.3%,and the content of COD decreased 78.8%after treated by a three-step method(filtration-heating-filtration).It is obvious that filtration-heating-filtration is an effective method to improve the purity of waste sulfuric acid.(2)Four gypsum samples were prepared,and the compositions of the gypsum samples were analyzed by elemental analysis,XRD,TG-DSC and standard weight method.The result showed that the content of CaSO4·2H2O in the gypsum sample prepared from treated waste sulfuric acid was 96.7%.Effect of gypsum content(1?5%)on the properties of cement,such as setting time,stability,flexural strength and compressive strength,were studied.Compared with the gypsum obtained from waste sulfuric acid,the 3 d and 28 d strength of cement was greatly improved when gypsum obtained from treated waste sulfuric acid was used as additive.Simultaneously,the conditions of gypsum preparation from treated sulfuric acid and carbide slag,as also as the amplification effect,were further studied.(3)A process for the treatment of waste sulfuric acid and production of gypsum was established in a chemical enterprise in northern Shaanxi province.Seven gypsum samples were randomly selected to analysis their compositions.The result showed that the content of CaSO4·2H2O in gypsum product was more than 95.8%.Properties of the cement prepared by the addition of different groups of gypsum were tested.The properties of cement were stable and they met the requirement of cement grade 32.5.The process for the production of gypsum from waste sulfuric acid can be operated stablely,and the quality of product is good,so the process is of strong promotion and application value... |
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