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

• Published in: Cement and concrete research Vol. 33; no. 8; pp. 1223 - 1227
• Main Authors: Potgieter, J.H., Potgieter, S.S., McCrindle, R.I., Strydom, C.A.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Ltd 01-08-2003; Elsevier Science
• Subjects: Applied sciences; Buildings. Public works; Cement concrete constituents; Cement manufacture; Cements; Composition (specifications, compliance criterid, standards, certification, control, patents, etc.); Compressive strength; Exact sciences and technology; Materials; Phosphogypsum; Retardation; Waste management; Waste management; Compressive strength; Phosphogypsum; Retardation; Cement manufacture; Physical dressing; Chemical treatment; Formulation; Cement; Experimental study; Setting time; Set retarder
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/S0008-8846(03)00036-X

The work describes various physical and chemical treatments to eliminate the deleterious effects of impurities in phosphogypsum on the delayed setting time and impaired strength development behaviour of cement to which it was added as a set regulator. The physical treatments included washing, milling, and ultrasonic treatment of the material, while the chemical treatments dealt with acidic and basic additions to the phosphogypsum during the washing stage. It was found that chemical treatment with a milk of lime solution, which is often recommended in literature, was ineffective in reducing set retardation. Treatment with ammonium hydroxide or sulphuric acid was more effective in this regard. Intergrinding phosphogypsum with slaked lime improved its effectiveness in reducing set retardation, but the use of unslaked lime was less effective and also resulted in marked reductions in compressive strengths. A combined treatment of wet milling phosphogypsum with a lime slurry in a ball mall was derived from these experiments and is recommended for full-scale plant applications.