Abstract

The existing α‐hemihydrate gypsum preparation process has low production efficiency and high energy consumption. In this paper, α‐type hemihydrate gypsum was prepared by microwave irradiation using phosphogypsum as the raw material, calcium chloride solution as the reaction medium, and succinic acid and aluminum sulfate as crystal‐transforming agents. Both aluminum sulfate and succinic acid were studied to determine the mechanism influencing the effect on the growth of α‐type hemihydrate gypsum crystals. This study found that, without added succinic acid or aluminum ions, the crystal transformation rate of α‐calcium sulfate hemihydrate reached 96% with the average length‐diameter ratio reaching 21 after 1 h; when the dosage of succinic acid was 0.02%, the crystal transformation rate of α‐calcium sulfate hemihydrate reached 96% with the average length‐diameter ratio reaching 1.5 after 1.5 h; and when the aluminum ion dosage was 5 mM, the crystal transformation rate of α‐calcium sulfate hemihydrate reached 97% with the average length‐diameter ratio reaching 12.3 after 1 h. In addition, it was discovered that the reaction time was significantly shortened under microwave irradiation, and with an increase in succinic acid content, the regulation of the microscopic morphology of the calcium sulfate hemihydrate crystals was continuously enhanced and the aspect ratio of the crystals was continuously reduced. The EDS and Fourier transform infrared spectroscopy (FTIR) analysis showed that succinic acid did not adsorb onto the hemihydrate gypsum crystal during the reaction under microwave irradiation. The X‐ray photoelectron spectroscopy (XPS) analysis revealed that aluminum ions affected crystal growth by incorporating into calcium sulfate hemihydrate crystals after reacting with sulfate radicals.

Highlights

  • Phosphogypsum (PG) is a solid waste product that is discharged during wet phosphoric acid production processes

  • The annual global production of PG is approximately 170 million tons, and the comprehensive utilization rate is approximately 5% [1]. e massive accumulation of PG has created many environmental problems, such as encroachment on land, soil pollution, and destruction of ecology, which have aroused widespread social attention. Resourceful remediation of these issues has become one of the main obstacles restricting the sustainable development of phosphorus chemical enterprises. e main component of PG is calcium sulfate dihydrate, which usually accounts for more than 85% of the total mass of the ideal raw material for the preparation of α-calcium sulfate hemihydrate

  • Using scanning electron microscopy (SEM), X-ray diffraction (XRD), EDS, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), the effects and mechanisms of reaction time and conversion rate, the crystal morphology, and the image composition of the reaction system were analyzed, which provided important basic data and technical guidance for industrial production of α-calcium sulfate hemihydrate under microwave irradiation of PG. e results provide a data-based foundation for studying the effect of crystallizer on the growth of α-calcium sulfate hemihydrate crystals under microwave irradiation

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Summary

Introduction

Phosphogypsum (PG) is a solid waste product that is discharged during wet phosphoric acid production processes. Α-calcium sulfate hemihydrate was prepared by microwave irradiation instead of by the traditional heating method, with PG as the raw material and calcium chloride solution as the reaction medium. Using scanning electron microscopy (SEM), X-ray diffraction (XRD), EDS, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), the effects and mechanisms of reaction time and conversion rate, the crystal morphology, and the image composition of the reaction system were analyzed, which provided important basic data and technical guidance for industrial production of α-calcium sulfate hemihydrate under microwave irradiation of PG. E results provide a data-based foundation for studying the effect of crystallizer on the growth of α-calcium sulfate hemihydrate crystals under microwave irradiation Using scanning electron microscopy (SEM), X-ray diffraction (XRD), EDS, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), the effects and mechanisms of reaction time and conversion rate, the crystal morphology, and the image composition of the reaction system were analyzed, which provided important basic data and technical guidance for industrial production of α-calcium sulfate hemihydrate under microwave irradiation of PG. e results provide a data-based foundation for studying the effect of crystallizer on the growth of α-calcium sulfate hemihydrate crystals under microwave irradiation

Materials and Methods
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