独居石碱分解热力学研究

Thermodynamics of alkali decomposition of monazite

独居石是一种轻稀土含量丰富的磷酸盐稀土矿,热碱浸出法对独居石的分解率可达97%,具有较高的经济效益℃。目前关于独居石碱分解的理论相对较少,缺少对独居石中稀土元素(Ce、Pr、Nd)的转变规律研究。本文通过热力学计算,绘制了25℃与160℃温度条件下碱分解独居石RE-P-H_(2)O体系(RE为La、Ce、Pr、Nd)溶解组分lgc-pH平衡图,并利用热力学平衡相图对碱分解独居石进行分析,结果表明:25℃条件下,在所研究的pH值范围内,LaPO_(4)固相稳定存在的区域为0.08<pH<14.62,REPO_(4)(RE为Ce、Pr、Nd)固相稳定存在的区域为0<pH<14.62;当pH≥14.62时,Pr(OH)_(3)、Ce(OH)_(3)、La(OH)_(3)、Nd(OH)_(3)依次沉淀的pH值为14.62、15.06、15.24、15.46;体系温度升高至160℃后,RE(OH)_(3)初始沉淀pH值降为10.70,沉淀顺序依次为Ce(OH)_(3)、Nd(OH)_(3)、La(OH)_(3)、Pr(OH)_(3)。因此,从理论分析可知,常温常压下可以实现独居石碱分解,高温高压条件对该分解过程有明显促进作用,与现有独居石碱分解工艺相符。

Monazite is a phosphate rare earth ore with abundant light rare earth content.The decomposition rate of monazite by hot alkali leaching method can reach 97%,which has high economic benefits.At present,there are relatively few theories on the alkali decomposition of monazite,and there is a lack of research on the transformation laws of rare earth elements(Ce,Pr,Nd)in monazite.This article uses thermodynamic calculations to draw the lgc-pH equilibrium diagram of the dissolved components of alkali decomposed monazite RE-P-H_(2)O system(RE is La,Ce,Pr,Nd)under temperature conditions of 25℃and 160℃.The thermodynamic equilibrium phase diagram is used to analyze alkali decomposed monazite.The results show that at 25℃,within the pH range studied,the region where LaPO_(4)solid-phase stability exists is 0.08<pH<14.62,The region where REPO_(4)(RE is Ce,Pr,Nd)solid-phase stability exists is 0<pH<14.62;When pH≥14.62,the pH values of Pr(OH)_(3),Ce(OH)_(3),La(OH)_(3),and Nd(OH)_(3)precipitated sequentially are 14.62,15.06,15.24,and 15.46;after the system temperature increased to 160℃,the initial precipitation pH of RE(OH)_(3)decreased to 10.70,and the precipitation order was Ce(OH)_(3),Nd(OH)_(3),La(OH)_(3),Pr(OH)_(3).Therefore,from theoretical analysis,it can be seen that the alkaline decomposition of solitary stones can be achieved at room temperature and pressure,and the high-temperature and high-pressure conditions have a significant promoting effect on this decomposition process,which is consistent with the existing alkaline decomposition process of solitary stones.