Abstract
Phosphogypsum (PG) is a massive industrial solid waste. In this paper, PG was purified by flotation method, and α-hemihydrate gypsum (α-HH) was prepared by the autoclaving method. The morphology of α-HH was adjusted by adding different doses of Maleic acid and Aluminium sulfate. The results showed that after flotation purification, the impurity content in PG was significantly reduced, the soluble phosphorus content decreased from 0.48 to 0.07%, the PG purity increased from 73.12 to 94.37%, and the PG whiteness risen from 19.4 to 40.5. Then the performance of α-HH prepared from PG before and after purification was compared. Fixing the amount of aluminium sulfate at 0.2 wt%, the reaction temperature at 140 °C, and the reaction time at 120 min, the average length/diameter ratio of α-HH crystals decreased from 7.2 to 0.6 as the amount of Maleic acid increased from 0 to 0.17 wt%. When the amount of Maleic acid was 0.13 wt%, the α-hemihydrate gypsum reached the best mechanical properties. The mechanical strength of high strength gypsum prepared from PG concentrate was significantly better than that of raw PG, indicating that flotation purification can effectively improve the performance of PG. In this study, a new method of PG purification and resource utilization was proposed.
Highlights
Phosphogypsum (PG) is a massive industrial solid waste
It can be inferred that the carboxylate anion in Maleic acid located at 3440 cm−1 formed a complex with Ca2+ on the top surface of the crystal, which further verified the interaction between the modifier and the α-hemihydrate gypsum (α-HH) crystal
The PG raw ore was purified using the flotation method, and α-HH with different crystal shapes was prepared by hydrothermal reaction
Summary
It can be seen that with the increase of MIBC dosage, the removal rate of organic impurities and slime, the whiteness and purity of PG concentrate increased. After the grinding and reverse flotation of PG to remove easy to float organic impurities and fine slime, it still contains some impurity minerals, mainly some coarse size of calcium phosphate stone These impurities still affect the PG whiteness, and elemental phosphorus, etc. Since the surface of CaSO4·2H2O is negatively charged in most of the pH range, the cationic collector has good collecting ability for it[42] In this experiment, dodecylamine was selected for the separation and purification of PG, and the effect of dodecylamine dosage on the whiteness and purity of gypsum was investigated. The unmodified α-HH crystals should be adjusted to smaller length and diameter crystals to improve their strength and performance
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