Research On The Comprehensive Recovery And Utilization Technology Of The By-salt In Desulfurization Liquid

During the absorption and regeneration process of desulfurization solution,by-salts such as thiosulfate,thiocyanate and sulfate will be generated.Under normal circum-stances,the content of biosalts needs to be controlled within a certain range,because too high a content of biosalts will increase the solution density and power consumption,leading to increased corrosion of equipment and pipelines,which may lead to system breakdown in serious cases.If there is a technical method to extract the desulfurization liquid by-salt and maintain its stable by-salt content without external discharge,it will help to reduce material loss,environmental protection and stable operation of equip-ment.Therefore,the comprehensive recovery and treatment of desulfurization fluid by-salt has not only environmental value but also potential economic value.In this study,copper sulfate pentahydrate was prepared from acidic copper chloride etching waste solution,which was used to treat sodium thiocyanate and sodium thio-sulfate as biosalts in the desulfurization solution,and then hydrogen peroxide was used to oxidize even sodium tetrasulfate in the treated desulfurization solution to sodium sulfate,and finally sodium sulfate was extracted by evaporation crystallization.This method can prepare products such as copper sulfate and cuprous thiocyanate with high added value while treating acidic copper chloride etching waste solution and desulfuri-zation solution by-salt.The products were characterized by X-ray diffraction analysis(XRD),thermogravimetric analysis(TG),Fourier infrared spectroscopy(FT-IR)and scanning electron microscopy(SEM)during the experiments.The main findings of this study are as follows.(1)The optimum process conditions determined for the production of copper oxide intermediates from acidic copper chloride etching waste solution were:the reaction temperature was 60°C and the p H of the reaction system was adjusted to 11.5.The results of chemical analysis showed that the purity of the copper oxide product reached99.24%and the chlorine content was about 110 ppm,which met the requirements of Cu O980 in the standard for copper oxide powder.The XRD analysis results showed that the resulting copper oxide product had a single composition.(2)The optimum process conditions for the production of copper sulfate pentahy-drate from copper oxide as an intermediate were determined as follows:the solid-liquid ratio of copper oxide to water was 1:3,the amount of concentrated sulfuric acid was105%of the theoretical value,the reaction was carried out at 70°C for 10 min,then cooled naturally to room temperature,crystallized for 4 h and then filtered,and the resulting filter cake was dried at 35°C for 2 h.The results of chemical analysis showed that the purity of the product obtained under this condition reached.The chemical anal-ysis results showed that the purity of the product obtained under this condition was99.04%and the chlorine content was about 40 ppm,which met the requirement of su-perior product in the industrial copper sulfate standard.(3)The optimum process conditions for the preparation of cuprous thiocyanate prod-ucts from copper sulfate pentahydrate by treating the desulfurization solution biosalt were determined as follows:the desulfurization solution was added to the copper sulfate solution,the reaction p H was about 4,the system was adjusted with n(Cu SO₄):n(Na₂S₂O₃):n(Na SCN)=1:1:1,the reaction temperature was room temperature,the re-action time was 0.5 h,and the product was dried at 105°C for 2 h.The chemical analysis results showed that this condition was the best.The results of chemical analysis showed that the removal rate of Na₂S₂O₃ and Na SCN from the desulfurization solution under this condition was more than 99%;the purity of the cuprous thiocyanate product reached 99.21%,which met the requirement of superior product in the enterprise stand-ard.The SEM analysis results showed that the size of the obtained cuprous thiocyanate products was about 50-300 nm with irregular morphology.(4)The method of preparing sodium sulfate by oxidizing sodium tetrasulfate with hydrogen peroxide was investigated,and the optimum process conditions were deter-mined as follows:the addition of oxidant was 2.5 times of the theoretical value,the reaction p H was about 8,the reaction temperature was 60?,and the reaction time was10 min.The results of chemical analysis showed that the sodium tetrasulfate in the treated desulfurization solution could be completely oxidized to sodium sulfate under this condition,and the product purity was obtained by evaporation and concentration and cooling crystallization.The purity of the sodium sulfate product obtained by evap-oration and crystallization reached 98.6%,which meets the requirement of Class II product in the industrial anhydrous sodium sulfate standard.the results of XRD analysis show that the resulting sodium sulfate product has a single composition.(5)The results of economic benefit estimation showed that the process of producing cuprous thiocyanate products by treating the desulfurization liquid by-salt with indus-trial copper sulfate could generate good economic benefits;the results of environmental analysis showed that the process was a clean and environmentally friendly process.