Fundamental Study On Separation Of Light Rare Earth Elements In P₂₀₄-HCl-H₃AOH System

Since the rare earth (RE) products have particular physical and chemical properties, they are widely used in metallurgy, petrochemical industry, various functional materials and glass ceramic field etc. In order to obtain individual rare earth element or mixed several rare earth elements from mixed rare earth feed, P204 or P507 as extractant saponified by ammonia liquor or ammonium acid carbonate are used to separate rare earth elements, but this method produces drain water contained high concentration NH4+, which heavily give environment pollution.In this thesis, the coordination agent citric acid (H3AOH) is added to rare earth and the unsaponified P204 is used as extractant in order to improve the process of separating light rare earth. The distribution ratio of rare earth elements in rare earth chloride solution and P204 extractant, separation coefficient, saturated extraction capacity and acidity, citric acid concentration, rare earth concentration were studied. The mechanics and the kinetics of the light rare earth extraction were studied.Under the conditions of different rare earth feed, acidity and citric acid concentration, the distribution ratio of the light rare earths and extraction saturated capacity in P204-HCl-H3AOH system were studied by single stage extraction experiments. The ternary linear regression equation of feed acidity, citric acid concentration and rare earth concentration was obtained, and the effect of them on the distribution ratio and separation coefficient were analyzed. The results show that, when feed acidity pH 1.0, citric acid concentration 0.25mol·L-1 and rare earth concentration 0.25mol·L-1, the max distribution ratio(D) comes up to DLa=0.1767, DCe=0.7353, DPr=1.5221 and DNd=2.4201 respectively, the max separation coefficient(β) areβCe/La=4.16,βpr/Ce=2.07 andβNd/Pr=1-59 respectively. By continuous stage extraction, the average separation coefficient of areβCe/La=3.50,βpr/Ce=2.05 andβNd/Pr=1-35 respectively at the same experiments conditions as single stage extraction, which are higher compare to the saponified P204 systemβCe/La=2.14,βPr/Ce=1-67 andβNd/Pr=1-33. Moreover, the capacity of unsaponified P204 extracting rare earth increases with citric acid concentration, its maxium is 29.71 g·L-1, which increases nearly 50% compare to soaponified P204.The extraction equilibrium constants(K) of unsaponified P204 in the citric acid system are 1gKLa=-1.77, 1gKCe=-1.63, 1gKPr=-1.26, 1gKNd=-0.86 when pH>1; and 1gKLa=-0.61,1gKCe =0.13,1gKpr=0.40,1gKNd=0.80 when 01. When 0