Investigation on a New Hydraulic Cementitious Binder Made from Phosphogypsum

Abstract

A new kind of high strength cementitious material is made from phosphogypsum (PG), active carbon and fly-ash. Through the orthogonal research, it was showed that the calcination temperature, retention time, dosage of active carbon and fly ash on the compressive strength of cementitious binder are the most important. The result also showed that, in the conditions of temperature 1200°C, time retention 30 min, dosage of active carbon 10%, dosage of fly ash 5%, the compressive strength of the cementitious material for 3d and 28d could reach to 46.35MPa and 92.70MPa, the content of sulfur trioxide was 11.60% accordingly. A lot of active mineral materials, such as dicalcium silicate, tricalcium silicate, tricalcium aluminate were formed in the calcination. The C-S-H gel, calcium hydroxide and ettringite were found in 3d and 28d hydrates. It is found that the lime saturation ratio and silica modulus need to be control between 0.40~0.65 and 4~8 in order to produce high strength cementitious material.

Process Optimization and Mechanism Study for Sulfur Recovery from High-Silica Phosphogypsum via Carbothermal Reduction Smelting

“…This reduced the content of Si, Al, Na, F, Cl, and other elements so that the lowest eutectic point of the raw materials was >1200 °C . The process of preparing cementitious material with phosphogypsum-activated carbon and relatively small fly ash was developed in which the optimum operating temperature was set at 1200–1250 °C and phosphogypsum was partially decomposed to improve the easy burning properties of the material . These operations alleviated the problem of kiln ringing owing to the formation of low-melting-point phases by lowering the operating temperature; however, this causes incomplete phosphogypsum decomposition.…”

“… 26 The process of preparing cementitious material with phosphogypsum-activated carbon and relatively small fly ash was developed in which the optimum operating temperature was set at 1200–1250 °C and phosphogypsum was partially decomposed to improve the easy burning properties of the material. 27 These operations alleviated the problem of kiln ringing owing to the formation of low-melting-point phases by lowering the operating temperature; however, this causes incomplete phosphogypsum decomposition. Additives were added to increase the melting characteristics of the material to avoid kiln ringing during the firing of the cement clinker.…”