摘要
氧化钙沉淀富集离子型稀土浸出液,具有成本低、收率高、能与镁盐复合浸取技术相衔接的优点,可实现离子吸附型稀土矿绿色提取。但是在氧化钙正加料沉淀稀土浸出液的过程中会产生大量的碱式硫酸稀土,导致混合稀土氧化物的SO_(4)^(2-)含量超标。针对这一问题,本文通过组贡献法热力学计算和氧化钙加料方式实验验证了在高碱度条件下过量氢氧根与硫酸根会进行竞争配位,将有效减少碱式硫酸稀土的生成。然后,实验研究获得了氧化钙反加料沉淀的最佳工艺条件,即氧化钙浆液浓度0.311 mol·L^(-1)、终点pH=9.0、反应温度24℃、稀土料液浓度0.93 g·L^(-1)、加料速度40 ml·min^(-1);此时得到的混合稀土氧化物纯度仅为89.7%,SO_(4)^(2-)含量为8.40%。为此,进一步采用氢氧化钠搅洗氧化钙反加料的沉淀产物,获得了纯度为95.43%,SO_(4)^(2-)含量为1.22%的混合稀土氧化物,可满足国标要求。基于此,提出了氧化钙反加料沉淀-氢氧化钠搅洗新工艺,该工艺可以省去传统除杂过程,回收铝资源、解决氧化钙沉淀过程中硫酸根引入的问题。本文的研究为稀土浸出液的无氨沉淀提供了新的思考,对离子吸附型稀土矿的绿色高效提取有重要的意义。
Ammonium sulfate leaching and ammonium bicarbonate precipitation enrichment process were currently used to recover rare earth from ionic type rare earth ore,and then roasted to obtain mixed rare earth oxides.However,the serious pollution with excessive ammonia nitrogen and eutrophication in the water system of the mining area had been caused by the large-scale applications of ammonium bicarbonate in the past decades years.An ammonia-free enrichment procedure of ionic type rare earth leaching solution was achieved by a positive feeding method of calcium oxide,which could avoid ammonia nitrogen pollution in the precipitation.Besides,the advantages of low consumption of precipitant and high recovery efficiency of rare earth were both possessed in the calcium oxide precipitation process.More importantly,an environment-friendly circulation of calcium ions between leaching and precipitation was an effective supplement for the consumption of the composite leaching agent in the in-situ leaching process by the Mg-Ca compound leaching agent,which established a tightly link from magnesium salt extraction to calcium oxide precipitation.However,a large amount of alkaline rare earth sulfate produced in the precipitation process of rare earth leaching solution by calcium oxide positive feeding,which caused the content of SO_(4)^(2-)in the mixed rare earth oxides to over 14%and exceeded the standard.To solve this problem,the thermodynamic calculation based on the group contribution method was carried out first.The results showed that the formation of alkaline rare earth sulfate could be suppressed in the presence of excess hydroxide,and a further transformation from the generated alkaline rare earth sulfate to rare earth hydroxide was thermodynamically feasible.The rare earth leaching solution used in this article was prepared in the laboratory from the composition of the rare earth leaching solution after impurity removal.And a pH meter was used to monitor the pH change during the reaction.The feeding was terminated while the pH reached the specified pH(terminal pH)in the system,and the stirring was to be continued in 5 min before solid-liquid separation.Mixed rare earth oxides were obtained after a roasting process applied to the precipitated product for 2 h in a muffle furnace at 800℃.The purity of the mixed rare earth oxides was determined by ethylene diamine tetraacetic acid(EDTA)complex ometric titration that the solution used for analysis was prepared by adding hydrogen peroxide and hydrochloric acid into mixed rare earth oxides followed by dissolving in heating.And the sulfate content was determined by a high-frequency infrared carbon-sulfur analysis meter.The quality of product was evaluated by the rare earth purity and sulfate content of the mixed rare earth oxides.Changes in the process parameters were taken and their impacts on product quality were researched,and the selection of best conditions was based on the improved product quality by stepwise optimization.The maintenance of the highly alkaline environment during the precipitation reaction showed a critical effect on the purity of the product and the content of sulfate.A higher terminal pH was required to provide a highly alkaline environment throughout the reaction and inhibit the formation of alkaline rare earth sulfate.The precipitation reaction efficiency was worsened by any factor that interfered with the maintenance of the high alkaline environment,the increment of temperature and concentration of rare earth reduced the solubility of calcium hydroxide and accelerated the consumption of hydroxide ions,respectively.Finally,the optimum conditions for the calcium oxide reverse feeding precipitation were obtained;namely,the concentration of calcium oxide slurry was 0.311 mol·L^(-1),terminal pH was 9.0,reaction temperature was 24℃,concentration of rare earth liquid was 0.93 g·L^(-1),and feeding speed was 40 ml·min^(-1).Under this condition,the purity of the mixed rare earth oxides and the content of SO_(4)^(2-)was respectively 89.7%and 8.40%,which was still lower than the national standard.The sulfate radical was in the form of rare earth sulfate oxysalts in the mixed rare earth oxides and an unsuccessful attempt at removing it by calcination was performed at 800℃.The unrealistic calcination temperature of 1400℃was required to remove the remaining sulfate radicals.Enhanced hydrometallurgical procedures are the preferred strategy for residual sulfate radical removal in the post-treatment step,just a more severe alkaline environment would be required.Therefore,sodium hydroxide was further used to agitation wash the products precipitated by calcium oxide reverse feeding process.In this way,mixed rare earth oxides with purity of 95.43%and SO_(4)^(2-)content of 1.22%were acquired.Based on this,a new process with calcium oxide reverse feeding precipitation and sodium hydroxide agitation washing process was proposed.This process could eliminate the traditional impurity removal process,recover aluminum resources,and solve the problem of sulfate radical introduction in the calcium oxide precipitation process.This study provided a new consideration for ammonia-free precipitation of rare earth leaching solution,and was of great significance for the green and efficient extraction of the ion-adsorption type rare earths ore.
作者
赖安邦
贺强
邱江
许城
肖燕飞
Lai Anbang;He Qiang;Qiu Jiang;Xu Cheng;Xiao Yanfei(Faculty of Materials Metallurgy and Chemistry,Jiangxi University of Science and Technology,Ganzhou 341000,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2021年第7期866-878,共13页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(51964018)
中国博士后科学基金资助项目(2018T110661)
江西省重点研发计划项目(20171ACE50008)
赣州市科技计划项目重点研发计划项目(赣市财教字[2017]179号)
赣州市科技创新人才计划项目(赣市科发[2018]50号)
江西省博士后科研项目择优一等资助项目(2018KY01)
江西理工大学清江青年英才计划项目(JXUSTQJYX2018003)资助。
关键词
反加料
组贡献法
稀土浸出液
氧化钙
碱式硫酸稀土
reverse feeding
group contribution method
rare earth leaching solution
calcium oxide
alkaline rare earth sulfate
