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The filtrate from lead paste desulfurization with citric acid contains desulfurizer citricacid, sodium citrate, which added excess,and sodium sulfate as product. As a purpose ofreducing process costs and realizing the industrial applications, it is an effective mean tofractional crystallizate sodium sulfate in filtrate and reuse the desulfurizer at process. Onthe base of experimental studies, the influence of sodium sulfate content in crystal bydifferent fractional crystallization methods is discussed and the method of fractionalcrystallization sodium sulfate from filtrate is proposed. The research achievements are asfollows:(1) The main component of lead paste is PbSO4, PbO2, PbO, and the proportion is65.0%,29.5%,4.5%respectively. The suitable conditions for lead paste leaching are atroom temperature, the ratio of actual amount to theory amout is.=1, the ratio of solid andliquid is1:5, the reaction time is24h.(2) According to analysis of the components of filtrate from lead pastedesulfurization, it shows that the filtrate is mixture with citric acid, sodium citrate andsodium sulfate. The density of filtrate is1.095g/ml, and the concentration of Na2SO4is25.25mg/ml, mass fraction2.30%corresponding. It meets SO42-balance for the proportionof output and input on SO42-is100%.(3) Experiment of fractional crystallization shows that evaporation solvent is notsuitable for sodium sulfate crystallization because the mass fraction of sodium sulfate incrystal is only1.58%. When the filtrate is heated, controlling the temperature and pH,impurity ions will interfere crystallization phenomenon, so it is important to chooseappropriate temperature range.(4) Though cycling filtrate, sodium sulfate is enriched, mass fraction increasing from1.23%to10.85%. This method has advantages of economical and simple, but it has little influence to crystallize sodium sulfate at room temperature.(5) The results from controlling crystal temperature shows that when the temperatureis10, the mass fraction of sodium sulfate in crystal is97%; while at room temperature25, the citric acid and sodium citrate crystal with98%purity can be gotten.The methodof controlling crystal temperature can separate sodium sulfate effectively from the solutionwith citric acid and sodium citrate, realizing the purpose of resource utilization for filtratefrom lead paste desulfurization with citric acid.
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