Effects of impurities from phosphogypsum on the crystal growth of calcium sulfate hemihydrates

Abstract

The influences of organic compounds, supernatant, calcium phosphate and calcium fluoride on the morphology of calcium sulfate hemihydrate were investigated in hydrothermal conditions by using calcium sulphate dihydrate of analytical grade as the raw material, while the organic compounds and supernatant were obtained from phosphogypsum (PG). The influence of the supernatant on the crystal growth was greater than the organic compounds. The crystal diameter increased and the aspect ratio decreased, while the added amounts of calcium fluoride and calcium phosphate increased. The influence of calcium phosphate on the crystal growth was more obvious than with calcium fluoride. Extremely non-uniform whiskers were observed when the amount of calcium fluoride and calcium phosphate were 5 % and 3 % (w/%), respectively. Key words: phosphogypsum; calcium sulfate hemihydrate; crystal morphology; impurities Avtorji so v pri~ujo~em prispevku raziskovali vplive organskih spojin, plavajo~ih ostankov, kalcijevega sulfata in kalcijevega fluorida na morfologijo kalcijevega sulfat polhidrida v hidrotermalnih pogojih. Kot surovino so uporabili sulfat dihidrat anali-ti~ne~istosti. S to sintezo so dobili organske spojine in plavajo~e ostanke iz fosfatnega gipsa (PG). Vpliv plavajo~ih ostankov na rast kristalov je bil ve~ji kot vpliv organskih spojin. Premer kristalov je nara{~al, medtem ko je razmerje med dol`ino in premerom kristalov padalo z nara{~anjem dodatka kalcijevega fluorida oz. kalcijevega fosfata. Vpliv kalcijevega fosfata na rast kristalov je bil o~itnej{i kot vpliv jedavca (kalcijevega fluorida). Vlakna skrajno nepravilnih oblik so nastajala, ko je bila vsebnost kalcijevega fluorida in kalcijevega fosfata 5 % oz. 3 %.

Modified phosphogypsum used as reinforcing material in composites

“…As can be seen, the notched Izod impact strength of the specimen with 5 wt% PG was decreased dramatically to 6.41 KJ/m 2 . However, within the range of weight fractions studied (5,10,15,15,20,25, and 30 wt), the impact strength of the composite material decreased slightly with the addition of modified calcined PG. While further increased in specimens of PG content to 30 wt%, impact strength only decreased to 4.99 KJ/m 2 .…”

“…It can lead to serious pollution of the atmosphere and groundwater. [9][10][11] Because these harmful impurities limit the application of PG, its utilization rate is only 15%. 12 Pretreatment such as washing, lime neutralization, acid leaching, flotation, and calcination can reduce the adverse impact of impurities on the utilization of PG.…”

Reduction of phosphogypsum for SO2 production: Insights into the release characteristics of SO2 following the solid–solid reaction of CaS and CaSO4 under different atmospheres

“…Phosphogypsum (PG) is a by-product of wet process phosphoric acid production, which usually produces approximately 4.5-5 t of PG per ton of phosphate fertilizer. [1] PG is usually stockpiled in special areas, and only approximately 15% is recycled. [2,3] The main component of PG is CaSO 4 Á 2H 2 O, which contains soluble phosphorus, fluorine, organic matter, eutectic, and phosphorus among other harmful impurities.…”

“…[2,3] The main component of PG is CaSO 4 Á 2H 2 O, which contains soluble phosphorus, fluorine, organic matter, eutectic, and phosphorus among other harmful impurities. [1,4,5] Therefore, its comprehensive utilization in other industries is limited. Modified phosphogypsum (MPG) was developed to improve dewaterability of sewage sludge.…”