Recycling of phosphate tailings and acid wastewater from phosphorus chemical industrial chain to prepare a high value-added magnesium oxysulfate cement

Phosphate tailings (PT) and acid water, by-products of phosphorus chemical industrial chain, are usually identified as waste because they can hardly be reused in cement production. This paper proposes an approach of recycling solid waste PT and acid wastewater in preparing a high value-added magnesium oxysulfate (MOS) cement. Results show that the phosphorus in acid water promotes the formation of 5 Mg(OH)₂·MgSO₄·7H₂O (517) phase, thereby improving compressive strength of MOS cement. MOS cement prepared with undiluted acid water present excellent resistance to water and acid. The incorporation of calcined PT lowers the strength of MOS cement but improves the volume stability. The phosphorus and fluorine in acid water are effectively immobilized by the cement matrix. Moreover, recycling of PT and acid water to produce MOS cement not only largely consumes the waste and benefits the environment, but also reduces the cost of waste disposal and cement production.