EDTA浸出白钨矿的热力学分析

摘要

对EDTA浸出白钨矿进行了热力学分析.通过热力学计算,绘制了25℃下白钨矿在0.1 mol/L的EDTA溶液中各主要溶解组分的lgc-pH图,以及白钨矿在不同EDTA浓度下EDTA配离子Y<'4->和WO<,4><'2->的lgc-pH图.利用这些热力学平衡图对EDTA分解白钨矿的工艺条件进行了分析,结果表明:溶液中Y<'4->浓度直接影响白钨矿的分解,而Y<'4->浓度取决于体系EDTA浓度和pH值.EDTA浓度越高,Y<'4->浓度也相应地越高;随着pH值的增加,H<,4>Y将依次电离成H<,3>Y<'->、H<,2>Y<'2->、HY<'3->、Y<'4->,pH值越大,Y<'4->浓度也越高,但是碱度增加到一定时候,Y<'4->浓度基本不再变化.以EDTA浓度为1 mol/L为例,体系pH值从7开始增加时,Y<'4->浓度最初会急剧的增加,接着增加的速度变缓,pH值增加到大约11左右,Y<'4->浓度达到最大,此时EDTA主要以Y<'4->的形式存在,可以发挥最好的分解能力.碱度继续增加,Y<'4->浓度基本上不再变化,EDTA的分解能力也基本不再变化.碱度增加到15.8以后,体系中OH<'->对白钨矿的分解占主导,已经变成了碱分解.根据热力学分析结论,解释了前人研究中发现的pH值在9～13范围内变化时对EDTA浸出白钨的过程没有影响的实验现象.%This paper studies the thermodynamic behaviors about the leaching of scheelite using EDTA. The Igc-pH diagrams at 25 ℃ for containing ions when the total EDTA concentration being 0.1 mol/L are established according to thermodynamic calculation. The Igc-pH diagrams for complex ion Y4- and WO42- at different EDTA concentrations are also established. Using these diagrams, thermodynamic analysis is carried out to show the effect of technical conditions on EDTA decomposition of scheelite. It appears that the concentration of Y4- has direct effect on EDTA decomposition of scheelite. The concentration of Y4- depends on the concentration of EDTA and the pH value. The higher the concentration of EDTA is, the concentration of Y4- is correspondingly higher. As the pH value is getting higher, H4Y will gradually ionize into H3Y-, H2Y2-, HY3-, Y4-. The higher the pH value is, the concentration of Y4- is also higher. When the alkalinity increases to a certain point, the concentration of Y4- does not change any more. For example, when the concentration of EDTA is 1 mol/L, the pH value of the system begins to increase from seven. The concentration of Y4- increases sharply initially, then the pace of increasing becomes slower. When the pH value increases to about 11 or so, the concentration of Y4- reaches the maximum. At this time the EDTA mainly exist in the form of Y4-. It demonstrates the largest capacity to decompose scheelite. As the alkalinity increases continually, the concentration of Y4- stays the same and the decomposition ability of EDTA does not change any longer. If the alkalinity continues to increase from fifteen point eight, OH-will takes the dominant position to decompose scheelite.Correspondingly, the system changes to alkali decomposition. Based on the conclusion of thermodynamic analysis,the author has explained the experimental results in the previous studies that pH value dose not affect the course of leaching scheelite using EDTA when the pH value changes between nine and thirteen.