磷石膏制备高纯硫酸钙循环工艺Ⅰ:提取SO_4~(2-)除杂热力学研究
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摘要
循环利用化学试剂从磷石膏中提取SO_4~(2-)和Ca2+制备高纯硫酸钙,其中一个重要环节是用NaOH溶液分解磷石膏从中提取SO_4~(2-)得到Na_2SO_4溶液和Ca(OH)_2渣。在此过程中,热力学分析结果表明,磷石膏中的杂质主要进入Ca(OH)_2渣中,只有少量Si、Al杂质以Na_2SiO_3和KAlO_2的形式溶解进入Na_2SO_4溶液。通过绘制25℃下Na_2SO_4溶液中SiO_3~(2-)和AlO_2~-水解后各组分的热力学平衡图发现,采用控制Na_2SO_4溶液pH值的方法,可沉淀去除其中的Si、Al杂质。验证试验表明,硫酸钠溶液初始pH=13.20时,Al质量浓度为17.7 mg/L,Si质量浓度为53.41mg/L;将pH调至12左右时,溶液中已检测不出Al,Si去除率为8.48%;将pH调至7左右时,溶液中检测不出Al,Si去除率为75.89%。
Chemical reagents SO_4~(2-)and Ca~(2+) in phosphogypsum could be recycled to prepare high-purity calcium sulfate.A key step in this process is to decompose phosphogypsum using NaOH solution to obtain Na_2SO_4 solution and Ca(OH)_2 residue.In this decomposition process,thermodynamic analysis indicates that the majority of impurities enters into the residue phase Ca(OH)_2,with a small amount of Si and Al impurities end up in Na_2SO_4 solution in forms of Na_2SiO_3 and KAlO_2.Based on phase diagram at 25 ℃ for the Na_2SO_4-SiO_3~(2-)-AlO_2~- system,Si and Al impurities may be removed via precipitation by adjusting pH value of the Na_2SO_4 solution.In verification tests on an initial sodium phosphate solution of pH 13.2 with Al 17.7 mg/L and Si53.41 mg/L,when pH was adjusted to 12,no Al was detected in the solution with Si 8.48% removal.After solution pH was further lowered to 7,Al was still negligible in the liquid phase,but Si removal was increased to 75.89%.
Chemical reagents SO_4~(2-)and Ca~(2+) in phosphogypsum could be recycled to prepare high-purity calcium sulfate.A key step in this process is to decompose phosphogypsum using NaOH solution to obtain Na_2SO_4 solution and Ca(OH)_2 residue.In this decomposition process,thermodynamic analysis indicates that the majority of impurities enters into the residue phase Ca(OH)_2,with a small amount of Si and Al impurities end up in Na_2SO_4 solution in forms of Na_2SiO_3 and KAlO_2.Based on phase diagram at 25 ℃ for the Na_2SO_4-SiO_3~(2-)-AlO_2~- system,Si and Al impurities may be removed via precipitation by adjusting pH value of the Na_2SO_4 solution.In verification tests on an initial sodium phosphate solution of pH 13.2 with Al 17.7 mg/L and Si53.41 mg/L,when pH was adjusted to 12,no Al was detected in the solution with Si 8.48% removal.After solution pH was further lowered to 7,Al was still negligible in the liquid phase,but Si removal was increased to 75.89%.
引文
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[3]彭家惠,彭志辉,张建新,等.磷石膏中可溶磷形态、分布及其对性能影响机制的研究[J].硅酸盐学报,2000,28(4):309-313.
[4]魏大鹏,陈前林,金沙,等.磷石膏的工业应用及研究进展[J].贵州化工,2009,34(5):22-25.
[5]丁翼.铬化合物的生产与应用[M].北京:化学工业出版社,2003.
[6]冯金煌.磷石膏及其综合利用的探讨[J].无机盐工业,2001,33(4):34-36.
[7]徐爱叶,李沪萍,罗康碧.磷石膏中杂质及除杂方法研究综述[J].化工科技,2010,18(6):59-64.
[8]叶大伦,胡建华.实用无机物热力学数据手册(第2版)[M].北京:冶金工业出版社,2002.
[9]李华昌,符斌.实用化学手册[M].北京:化学工业出版社,2006.
[10]周连江,乐志强.无机盐工业手册(下)[M].北京:化学工业出版社,1996.
[11]Saxena S.K.,Chatterjee N.,Fei Y..Thermodynamic data on oxides and silicates:an assessed data set based on thermochemistry and high pressure phase equilibrium[M].New York:Springer-Verlag,1993.
[12]张吉清.含碱硅酸钠溶液合成硅酸钙基矿物材料的研究[D].长沙:中南大学,2012.
[13]J.H.Potgieter,S.S.Potgieter,R.I.McCrindle,et al.An investigation into the effect of various chemical and physical treatments of a South African phosphogypsum to render it suitable as a set retarder for cement[J].Cement and Concrete Research,2003,33:1 223-1 227.
[14]C.Papastefanou,S.Stoulos,A.Ioannidou,et al.The application of phosphogypsum in agriculture and the radiological impact[J].Journal of Environmental Radioactivity,2006,89:188-198.
[15]A.K.Nayak,D.K.Sharma,V.K.Mishra,et al.Effect of phosphogypsum amendment on fluoride content of soil and plants under rice(Oryza sativa)-wheat(Triticum aestivum)system in sodic soil of Indo-Gangetic plains[J].Indian Journal of Agricultural Sciences,2009,79(8):615-619.
[16]Denev Y.G.,Denev G.D.,Popov A.N..Surface modification of phosphogypsum used as reinforcing material in polyethylene composites[J].Journal of Elastomers and Plastics,2009,41(2):119-132.
[17]W.L.Charles.Silicate minerals as sources of trimethylsilyl silicates and silicates structure of analysis of sodium silicate solutions[J].Inorganic Chemistry,1964,3(4):574-579.
[18]P.Caullet,J.L.Guth.Zeolite synthesis[M].Washington,DC:1989.
[19]R.W.Harman.Aqueous solutions of sodium silicates.I.preparation and electric conductivity[J].Marine Chemistry,1983,13(1):35-44.
[20]R.N.MicheAl,W.S.Thomas.Kinetic of silicate exchange in alkaline alumina silicate solutions[J].Inorganic Chemistry,2000,39:2 661-2 665.
[21]E.R.Lippincott,J.E.Psellos,M.C.Tobin.The raman spectra and structures of aluminate and zincate ions[J].Chem.Phy,1952,20:536-541.
[22]李洁.过饱和铝酸钠溶液结构及分解机理的研究[D].长沙:中南大学,2001.
[23]Waltling,Helen.Sipos P M,et al.Spectroscopy of concentrated sodium aluminate solution[J].Appl.Spectrosc,1998,52(2):250-258.