Influence of the setting activators on the physical mechanical properties of phosphoanhydrite

Abstract

Phosphoanhydrite was obtained by processing dihydrate phosphogypsum generated during phosphoric acid production at Joint Stock Company (JSC) Lifosa (Lithuania). The influence on the properties of phosphoanhydrite of the treament process’ parameters was determined, including the conditions of phosphogypsum neutralisation in the lime suspension; temperature and duration of calcination of neutralized phosphogypsum to phosphoanhydrite; fineness of ground anhydrite; selection of additives activating the hydration of anhydrite and their amounts. Upon adding activators of anhydrite hydration, K2SO4 or Na2SO4, the data of XRD and IR spectral analysis show that the specimens after 1 day of phosphoanhydrite hydration with additives contain complex salts - syngenite upon using K2SO4 additive and glauberite in the case of Na2SO4 additive. These additives act as crystallization centers and accelerate hydration. It has been determined that the specimens of phosphoanhydrite calcined at a temperature of 900 º C with 2 % K2SO4 additive have the best physical and mechanical properties. Already after 1 day of hardening the specimens acquired a compressive strength of 21.18 MPa, and after 28 days of hardening they had a compressive strength of 58.5 MPa (dry specimens).

Keywords

• neutralized phosphogypsum
• phosphoanhydrite
• dihydrate calcium sulphate
• calcination
• potasium sulphate
• sodium sulphate