Crystallization Of Yttrium And Neodymium Carbonates And The Relative Technologies

The crystallization characterization of yttrium and neodymium carbonates, which are precipitated from yttrium or neodymium chloride solution with ammonium bicarbonate as precipitant, were investigated by means of pH value and deposit volume determination in situ, XRD, SEM and chemical analysis. The attention was paid especially on the effects of additives and crystallization conditions on the composition, phase type, morphology of crystalline yttrium or neodymium carbonate. The results show that:Crystalline yttrium carbonate Y₂(CO₃)₃·2H₂O with tengerite type structure was obtained by aging amorphous yttrium carbonate at 50 °C after its precipitation by ammonium bicarbonate with feed molar ratio NH₄HCO₃:YCl₃=2. Its SEM photograph shows that some irregular flakes grow out from acicular particle agglomerates. which indicates that the crystallization process may undergo the two dissolution- recrystallization processes: from amorphous precipitate to needle crystal and then from needle crystal to plate crystal. Furthermore, these needle or platelet crystals can all transfer to regulate grain particles during the further feeding and aging process. This fact indicates that there may exist multi dissolution-recrystallization processes, resulting in the morphology transformation from 1-D needle to 2-D flake, and then to 3-D regulate grain particle. A fast crystallization method of yttrium carbonate with large particle size is proposed.The addition of cerium ions in the suspension of amorphous yttrium carbonate after its precipitation by ammonium bicarbonate with feed molar ratio NH₄HCO₃:YCl₃=2 can promote the crystallization of yttrium carbonate at room temperature, forming tengerite type yttrium carbonate with large size particle agglomerated by acicular crystals. This promotion action is due to the preference necleus of cerium carbonate resulted from its preference adsorption on amorphous precipitate surface. After that, yttrium carbonate nucleus was formed by the second nucleation induced by cerium carbonate nucleus. The re-dissolution of cerium during the later aging process indicates that cerium ion has no effect on the further re-crystallization of yttrium carbonate.Neodymium carbonate can transfer from amorphous to crystalline normal neodymiumcarbonate Nd2(CO3)3-8H2O with lanthanide structure at room temperature. However, this transformation is very slow, but can be accelerated by seeding. The more seed is added, the faster crystallization speed is. The amorphous neodymium carbonate can crystallize directly with synchronously and continuously feeding manner under seeding. At the same time, the pH value during crystallization can be controlled within a narrow district, which is benefit for the producing of neodymium carbonate crystal with well-distribution particle size and monitoring of crystallization process.Crystalline neodymium carbonate Nd2(CC>3)3-2.5H2O with tengerite-type structure was synthesized using ammonium bicarbonate as precipitant at elevated temperature with feed molar ratio NUtHCOs/NdCb around 2.5. The addition of PGFAE can not only eliminate the foam formed during precipitation, but also shorten crystallization time, hold the basic crystallization characterization of one dimension growth, and form large radiative-like shape conglomeration by the irregulative linkage of one dimension needle crystals. It was also suggested that the morphology, the content of neodymium oxide and chloride ion in neodymium carbonate lie on its structure and crystal growth characterization. And tengerite type neodymium carbonate contains less crystalline water and chloride than that lanthanite type neodymium carbonate crystallized at room temperature do, which is benefit for the production of neodymium carbonate with higher neodymium and lower chloride content.