YANG Wei-ping1, ZHANG Xin1, ZOU Hang1, LI Xian-bo1,2,3 *

(1. Mining College, Guizhou University, Guiyang 550025, China;
2. National & Local Joint Laboratory of Engineering for Effective Utilization of Regional Mineral Resources from Karst?Areas, Guizhou University, Guiyang 550025, China;
3. Guizhou Key Lab of Comprehensive Utilization of Non-metallic Mineral Resources, Guizhou University, Guiyang 550025, China)

Abstract: Salt medium and crystal converting agent are critical factors for preparation of α-hemihydrate phosphogypsum (α-HPG) by using the atmospheric pressure salt solution method. The effects of maleic acid on crystal morphology, compressive strength and microstructure of hardened body of the α-HPG prepared in MgCl2 solution has been studied in this paper. The results show that the long-column α-HPG crystals can be prepared in MgCl2 solution, and the morphology of α-HPG crystal can be then regulated by adding maleic acid from the long column to the short column. With the increase of maleic acid concentration in MgCl2 solution, the length of α-HPG was shortened, the diameter of α-HPG was increased, and the length/diameter ratio of α-HPG was reduced. With the interaction of maleic acid, the crystal plane strengths of α-HPG (200), (020) and (400) planes were decreased, but the crystal plane strength of the (204) plane was increased. On the (200), (020) and (400) crystal planes, the Ca2+ cation is located between SO42- anions. There is a steric hindrance effect for the adsorption of maleic acid on the crystal planes of the α-HPG. There is no SO42- anion between Ca2+ cations on the (204) plane. The two COO- anions of maleic acid can interact with two Ca2+ cations to form a stable adsorption configuration which will hinder the growth of α-HPG along its length direction. When no crystal concerting agent was added, the hardened body of α-HPG has many relatively large sized internal pores and overall loose structure, with the compressive strength of only 12.5 MPa. When the concentration of added maleic acid is 1.08 mmol/L, the hardened body of α-HPG has compact texture, obviously reduced numbers of internal pores, with its maximum compressive strength of 26.5 MPa. The optimal maleic acid concentrations for the regulation of α-HPG vary from 0.54 mmol/L to 1.08 mmol/L.

Keywords: α-hemihydrate phosphogypsum; maleic acid; crystal morphology; compressive strength; microstructure

ACTA MINERALOGICA SINICA Vol. 43, No. 4, 2023, Page 558