Study On Extraction And Recovery Of H₃cit-LA From H₃cit-LA-LaCl₃system Using Tri-n-butylphosphate

In the traditional industry practices, it is widely recognized that the separation and purification of the neighboring rare earths is still known to be difficult due to their similar chemical and physical properties. Also, the extraction of rare earths in a saponated system will produce a large amount of waste water, which contains NH4+, Ca2+and Na+, and will seriously pollute environment. This paper aims to develop a new system to eliminate the phenomena. However, the complexing agents in the aqueous phase will result in the increase of COD value and the assumption that the complexing agents in the raffinate do not recover.In this paper, the extraction of La, Ce, Pr and Nd using the P204as an extractant in the presence of LA and extraction, we take the raffinate containing La and the complexing agents as the feed, using the TBP as an extractant, to recycle and concentrate the complexing agents with the method of solvent extraction.The experiments of recovering the complexing agents show that:the extraction rate increases with the extraction stages and the extractant concentrations. When the TBP concentration is3.68mol/L, temperature at25℃and pH0.6, the extraction rates are45%and65%, respectively. When the TBP concentration is2.76mol/L, temperature at25℃and pH0.6, the concentrations of LA and H3cit in the organic phase are0.42mol/L and0.045mol/L, respectively. At the same time, the COD value in the raffinate is determined as61.8mg/L, which meets the rare earth industry standards for pollutants discharge.The experiments of stripping the organic phase loaded the complexing agents show that: the stripping rates increase with the increasing of stripping stages and the decreasing of O/A. The enrichment tests using the deionized water as a stripping agent show that:when the O/A is2:1, stripping temperature at50℃, and stripping stages are8, the stripping rates are75%and90%, and the concentrations are enrichment to0.58mol/L and0.11mol/L, respectively. When the O/A is5:1, stripping temperature at50℃, and stripping stages are10, using the alkaline solution of pH13as a stripping agent, the stripping rates are nearly100%, and the concentrations are enrichment to1.4mol/L and0.54mol/L.The dependence of distribution ratio on temperature shows that:the extraction procedures TBP are exothermically driven.The ΔH values are calculated to be-6.7kJ·mol-1and-19.39kJ·mol-1, respectively. The neutral solvating extraction is clarified by IR spectra.The above experimental results relize the separation between light rare earths, and achieve the recovery and concentration of complexing agents, which is important for potential industrial applications.