MgCl_(2)溶液中顺丁烯二酸调控α半水磷石膏晶形

Regulation of crystal morphology of the a-hemihydrate phosphogypsum by using the maleic acid in MgCl_(2)solution

盐介质和转晶剂是常压盐溶液法制备α半水磷石膏的关键因素,本文研究了MgCl_(2)溶液中顺丁烯二酸对磷石膏制备α半水磷石膏晶体形貌、硬化体抗压强度及微观结构的影响。结果表明,在MgCl_(2)溶液中能够制备出长柱状α半水磷石膏,添加顺丁烯二酸能够调控α半水磷石膏的晶体形貌,使其从长柱状向短柱状转变。随着顺丁烯二酸浓度的增大,α半水磷石膏的长度缩短、直径增大、长径比降低。在顺丁烯二酸作用下,α半水磷石膏(200)、(020)和(400)晶面强度降低,(204)晶面强度增加。在(200)、(020)和(400)晶面上,Ca^(2+)位于SO_(4)^(2-)之间,顺丁烯二酸在表面上吸附存在空间位阻效应。(204)晶面上Ca^(2+)间不存在SO_(4)^(2-),顺丁烯二酸的2个COO-可以分别与2个Ca^(2+)作用形成稳定的吸附构型,阻碍α半水磷石膏沿长度方向生长。未添加转晶剂时,α半水磷石膏的硬化体内部孔洞较多,孔直径较大,整体较疏松,抗压强度只有12.5MPa;当顺丁烯二酸浓度为1.08 mmol/L,α半水磷石膏的硬化体结构致密,内部孔洞数量明显减少,抗压强度达到26.5 MPa,合适的顺丁烯二酸浓度为0.54~1.08 mmol/L。

Salt medium and crystal converting agent are critical factors for preparation ofα-hemihydrate phosphogypsum(a-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 theα-HPG prepared in MgCl_(2)solution has been studied in this paper.The results show that the long-columnα-HPG crystals can be prepared in MgCl_(2)solution,and the morphology of aα-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 MgCl_(2)solution,the length ofα-HPG was shortened,the diameter ofα-HPG was increased,and the length/diameter ratio ofα-HPG was reduced.With the interaction of maleic acid,the crystal plane strengths of aα-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 Ca^(2+)cation is located between SO_(4)^(2-)anions.There is a steric hindrance effect for the adsorption of maleic acid on the crystal planes of the aα-HPG.There is no SO_(4)^(2-)anion between Ca^(2+)cations on the(204)plane.The two C00°anions of maleic acid can interact with two Ca^(2+)ccaations to form a stable adsorption configuration which will hinder the growth ofα-HPG along its length direction.When no crystal concerting agent was added,the hardened body ofα-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 ofα-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 ofα-HPG vary from 0.54 mmol/L to 1.08 mmol/L.