碱法分解白钨矿的热力学研究
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摘要
工业上对白钨矿的碱法工艺一直在寻求强化途径,提高浸出剂浓度以降低试剂消耗就是途径之一。但工业上发现：用苏打浸出白钨矿时浓度不宜过高,一般不超过200g/L,苏联学者甚至指出浓度一旦超过230 g/L就会导致浸出率急剧下降；磷酸钠和氟化钠浸出白钨矿在工业上也有应用,一般也采用较低浓度。现有的理论无法对这一现象作出合理的解释。
本文利用赝三元相图作为分析手段,从热力学的角度对碱法分解白钨矿的过程进行了系统和深入的研究,查明了隐藏在它们背后的共同规律——盐析效应,建立了一个用于阐述浸出反应热力学问题的统一理论,具体研究内容如下：
(1)分别绘制了75℃和225℃下苏打分解白钨矿体系的赝三元相图,并对它们进行了详尽的分析,验证了理论预测,得出结论：苏打分解白钨矿的过程中,苏打浓度不宜过高是因为过高浓度会导致出现“盐析效应”,使得作为浸出剂的苏打从溶液里结晶析出,引起浸出反应逆向进行,造成溶液里钨浓度的回落,从而降低浸出率；
(2)利用苏打体系的赝三元相图对苏打分解白钨精矿的实验结果进行了分析,发现该图可以合理的解释实验结果,证明了该图的正确性和有效性；
(3)从苏打体系的赝三元相图上获取了逆反应过程的热力学信息,并对逆反应——钨酸钠分解碳酸钙进行了实验研究,发现与获取的信息相符：高的钨酸钠浓度有利于碳酸钙分解。进一步证明了苏打体系赝三元相图的正确性；
(4)沿用苏打体系的研究思路,绘制出230℃下磷酸钠分解白钨矿体系的赝三元相图,利用该图对浸出反应进行了热力学分析,发现与苏打体系类似的规律——过高磷酸钠浓度亦会导致“盐析效应”的出现,作为浸出剂的磷酸钠从溶液里结晶析出,造成浸出率的下降；利用该图对磷酸钠分解白钨精矿的实验结果进行了合理的解释,验证了该图的正确性和有效性；
(5)绘制出90℃下氢氧化钠分解白钨矿体系的赝三元相图；系统的比较和分析不同碱法提钨体系,发现“盐析效应”是隐藏在它们背后的共同规律；建立了一个能够对较广浓度范围内不同碱法提钨体系的热力学问题进行说明的统一理论；并利用该理论对氟化钠分解白钨矿体系进行了预测,发现高浓度氟化钠同样不利于浸出,与实际情况相符；
(6)利用赝三元相图对碱浸白钨过程中磷的行为进行了研究,发现：碱很难将磷从矿石中提取出来；在浸出液结晶的过程中,绝大部分磷停留在母液；母液中的磷会由于返回浸出时钙的存在而形成羟基磷酸钙以渣的形式排出体系,不会在溶液里形成积累。
The industry has been seeking to ways to enhance the technology of scheelite decomposition using alkali method; increasing concentration in order to reduce reagent consumption is one of the ways. But there is a strange phenomenon in the industry:when using soda to leach sheelite, the concentration should not be too high and it is generally less than 200 g/L, Soviet scholars even has pointed out that once it is more than 230 g /L, it will lead to a sharp decline in the leaching rate. Using sodium phosphate or sodium fluoride to leach scheelite also exists in the industry, and the concentration is also in a low level. The existing theory can not provide a reasonable explanation of this phenomenon.
Using pseudo-ternary diagram as an analysis means, the author has made a systematic and in-depth study about the process of alkali-by scheelite decomposition from the thermodynamics direction. The common law hidden behind different systems has been found, based on it, a unified theory which can describe the thermodynamics issue of leaching reaction has been established. The specific contents are as follows:
(1) The pseudo-ternary diagrams of soda-by scheelite decomposition system under 75℃and 225℃have been drawn. Detailed analysis of diagrams has been done, the prediction has been proved and some conclusions have been obtained:in the process of soda-by scheelite decomposition, the reason why leaching agent concentration should not be too high is that:too high concentration will lead to "salting out effect", which making the leaching agent separate out from the solution in the crystallization, then causing the leaching reaction reverse, thereby reducing the leaching rate;
(2) The experimental results of scheelite concentrate decomposition have been analyzed using the obtained pseudo-ternary phase diagram of soda system. It has been found that the diagram is reasonable to interpret the experimental results and it thereby proves the correctness and effectiveness of the diagram.
(3) The thermodynamics information of the reverse reaction can also be obtained from the pseudo-ternary phase diagram of soda system, and the reverse reaction—decomposition of calcium carbonate using sodium tungstate has been studied experimentally. It has been found that:high concentration of sodium tungstate benefit calcium carbonate decomposition which is consistent with the information obtained. It further proves the correctness of pseudo-ternary phase diagram.
(4) Following the study method of soda system, the pseudo-ternary diagrams of sodium phosphate-by scheelite decomposition system under 230℃have been drawn, by which, the thermodynamics analysis about leaching reaction has been done. It has been found that there exists a similar law in the sodium phosphate system:high sodium phosphate concentration will also lead to "salting out effect", which making the leaching agent separate out from the solution in the crystallization, then reducing the leaching rate. The experimental results of scheelite concentrate decomposition have been reasonably explained using the obtained pseudo-ternary phase diagram of sodium phosphate system and it thereby proves the correctness and effectiveness of the diagram.
(5) The pseudo-ternary diagrams of sodium hydroxide-by scheelite decomposition system under 90℃have been drawn. Comparing different scheelite leaching systems by alkali method, it has been found that "salting out effect" is the common law hidden behind different systems. A unified theory which can describe the thermodynamics issue of leaching reaction in a wide concentration scope has been established. Using the obtained theory, the sodium fluoride-by scheelite decomposition system has been predicted, it is found that high sodium fluoride concentration will also be harmful to the leaching reaction, which is corresponding to the actual situation.
(6) Using pseudo-ternary phase diagram, the behavior of phosphorus in the process of sheelite leaching by sodium hydroxide has been studied. It has been found that it is difficult to extract phosphorus from the ore using sodium hydroxide. In the crystallization process of leaching solution, the majority of phosphorus remains in the mother liquor. The remaining phosphorus will combine existing calcium to form calcium hydroxyapatite; thereby it will be discharged from the system in the form of slag. So it will do not accumulate in the solution.
本文利用赝三元相图作为分析手段,从热力学的角度对碱法分解白钨矿的过程进行了系统和深入的研究,查明了隐藏在它们背后的共同规律——盐析效应,建立了一个用于阐述浸出反应热力学问题的统一理论,具体研究内容如下：
(1)分别绘制了75℃和225℃下苏打分解白钨矿体系的赝三元相图,并对它们进行了详尽的分析,验证了理论预测,得出结论：苏打分解白钨矿的过程中,苏打浓度不宜过高是因为过高浓度会导致出现“盐析效应”,使得作为浸出剂的苏打从溶液里结晶析出,引起浸出反应逆向进行,造成溶液里钨浓度的回落,从而降低浸出率；
(2)利用苏打体系的赝三元相图对苏打分解白钨精矿的实验结果进行了分析,发现该图可以合理的解释实验结果,证明了该图的正确性和有效性；
(3)从苏打体系的赝三元相图上获取了逆反应过程的热力学信息,并对逆反应——钨酸钠分解碳酸钙进行了实验研究,发现与获取的信息相符：高的钨酸钠浓度有利于碳酸钙分解。进一步证明了苏打体系赝三元相图的正确性；
(4)沿用苏打体系的研究思路,绘制出230℃下磷酸钠分解白钨矿体系的赝三元相图,利用该图对浸出反应进行了热力学分析,发现与苏打体系类似的规律——过高磷酸钠浓度亦会导致“盐析效应”的出现,作为浸出剂的磷酸钠从溶液里结晶析出,造成浸出率的下降；利用该图对磷酸钠分解白钨精矿的实验结果进行了合理的解释,验证了该图的正确性和有效性；
(5)绘制出90℃下氢氧化钠分解白钨矿体系的赝三元相图；系统的比较和分析不同碱法提钨体系,发现“盐析效应”是隐藏在它们背后的共同规律；建立了一个能够对较广浓度范围内不同碱法提钨体系的热力学问题进行说明的统一理论；并利用该理论对氟化钠分解白钨矿体系进行了预测,发现高浓度氟化钠同样不利于浸出,与实际情况相符；
(6)利用赝三元相图对碱浸白钨过程中磷的行为进行了研究,发现：碱很难将磷从矿石中提取出来；在浸出液结晶的过程中,绝大部分磷停留在母液；母液中的磷会由于返回浸出时钙的存在而形成羟基磷酸钙以渣的形式排出体系,不会在溶液里形成积累。
The industry has been seeking to ways to enhance the technology of scheelite decomposition using alkali method; increasing concentration in order to reduce reagent consumption is one of the ways. But there is a strange phenomenon in the industry:when using soda to leach sheelite, the concentration should not be too high and it is generally less than 200 g/L, Soviet scholars even has pointed out that once it is more than 230 g /L, it will lead to a sharp decline in the leaching rate. Using sodium phosphate or sodium fluoride to leach scheelite also exists in the industry, and the concentration is also in a low level. The existing theory can not provide a reasonable explanation of this phenomenon.
Using pseudo-ternary diagram as an analysis means, the author has made a systematic and in-depth study about the process of alkali-by scheelite decomposition from the thermodynamics direction. The common law hidden behind different systems has been found, based on it, a unified theory which can describe the thermodynamics issue of leaching reaction has been established. The specific contents are as follows:
(1) The pseudo-ternary diagrams of soda-by scheelite decomposition system under 75℃and 225℃have been drawn. Detailed analysis of diagrams has been done, the prediction has been proved and some conclusions have been obtained:in the process of soda-by scheelite decomposition, the reason why leaching agent concentration should not be too high is that:too high concentration will lead to "salting out effect", which making the leaching agent separate out from the solution in the crystallization, then causing the leaching reaction reverse, thereby reducing the leaching rate;
(2) The experimental results of scheelite concentrate decomposition have been analyzed using the obtained pseudo-ternary phase diagram of soda system. It has been found that the diagram is reasonable to interpret the experimental results and it thereby proves the correctness and effectiveness of the diagram.
(3) The thermodynamics information of the reverse reaction can also be obtained from the pseudo-ternary phase diagram of soda system, and the reverse reaction—decomposition of calcium carbonate using sodium tungstate has been studied experimentally. It has been found that:high concentration of sodium tungstate benefit calcium carbonate decomposition which is consistent with the information obtained. It further proves the correctness of pseudo-ternary phase diagram.
(4) Following the study method of soda system, the pseudo-ternary diagrams of sodium phosphate-by scheelite decomposition system under 230℃have been drawn, by which, the thermodynamics analysis about leaching reaction has been done. It has been found that there exists a similar law in the sodium phosphate system:high sodium phosphate concentration will also lead to "salting out effect", which making the leaching agent separate out from the solution in the crystallization, then reducing the leaching rate. The experimental results of scheelite concentrate decomposition have been reasonably explained using the obtained pseudo-ternary phase diagram of sodium phosphate system and it thereby proves the correctness and effectiveness of the diagram.
(5) The pseudo-ternary diagrams of sodium hydroxide-by scheelite decomposition system under 90℃have been drawn. Comparing different scheelite leaching systems by alkali method, it has been found that "salting out effect" is the common law hidden behind different systems. A unified theory which can describe the thermodynamics issue of leaching reaction in a wide concentration scope has been established. Using the obtained theory, the sodium fluoride-by scheelite decomposition system has been predicted, it is found that high sodium fluoride concentration will also be harmful to the leaching reaction, which is corresponding to the actual situation.
(6) Using pseudo-ternary phase diagram, the behavior of phosphorus in the process of sheelite leaching by sodium hydroxide has been studied. It has been found that it is difficult to extract phosphorus from the ore using sodium hydroxide. In the crystallization process of leaching solution, the majority of phosphorus remains in the mother liquor. The remaining phosphorus will combine existing calcium to form calcium hydroxyapatite; thereby it will be discharged from the system in the form of slag. So it will do not accumulate in the solution.
引文
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