Study on solidification of soluble phosphorus in phosphogypsum by Ca/Al/La LDH
Phosphogypsum(PG)is a by-product of the wet phosphoric acid process which contains soluble phosphorous with a mass fraction of 1％to 2％.Stockpiling of large amount of PG will cause serious environmental issues.In this study,Ca/Al/La hydrotalcite(LDH)materials were synthesized by using mechanochemical method and then applied for the solidi-fication of the soluble phosphorus in PG.The effects of synthesis condition on solidification capacity were analyzed and the physiochemical characteristics of gypsum blocks using PG before and after treatment were compared.X-ray diffractometer(XRD),Fourier infrared spectrometer(FT-IR),scanning electron microscope(SEM)and particle size analyzer were ap-plied to explore the effects of the LDH-material dosage on soluble phosphorus solidification efficiency and PG microstruc-ture.The results showed that the optimal synthesis conditions were using 6％(volume fraction)ethanol as the dispersant with a molar ratio of n[Ca(OHI)2]∶n[AI(OH)3]∶n[La2(CO3)3·xH2O]=12∶6∶1,ball milling speed of 600 r/min,and ball milling time of 1 h,which showed best solidification effects on soluble phosphorus.With addition of 1 g/L of LDH materials,the so-lidification efficiency of soluble phosphorus in PG was up to 89.95％for Ca/Al/La LDH(ethanol),superior than Ca/Al LDH(78.70％)and Ca/Al/La LDH(80.86％).Ethanol enabled the LDH materials to be uniformly dispersed in PG and therefore could more effectively combine with soluble phosphorus,improving the solidification performance.The flexural and compres-sive strengths of gypsum blocks prepared using treated PG reached 6.60 MPa and 9.30 MPa,respectively,which were in ac-cordance with the standard of construction gypsum(level 2),and thus provided a feasible approach towards the harmless-ness and resourcefulness of PG.
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