Bismuth (Iii) Oxalates Obtaning By Precipitation From Nitric Acid Solutions

This paper describes the precipitation of bismuth (III) oxalates from industrial nitric acid solutions. The process was carried out by adding of oxalic acid depending on the molar ratio of oxalate ions to bismuth (n), reaction temperature and the acidity of solution. The existence of four different crystal structures in the precipitation products was confirmed by the methods of X-ray diffraction, IR spectroscopy in combination with chemical analysis of solid phases. The compound with composition Bi(C2O4) OH is precipitated from nitric acid solutions in a wide range of temperatures at n=1. Increasing n to 1.5 at room temperature leads to the formation of compound Bi-2(C2O4)(3)center dot 7H(2)O. The precipitation of octahydrate bismuth oxalate Bi-2(C2O4)(3)center dot 8H(2)O occurs when n = 2, process temperature of 80 degrees C and mixing time of 1 h. Further increasing in mixing time leads to recrystallization with formation of hexahydrate having the composition Bi-2(C2O4)(3)center dot 6H(2)O. Latter compound can also be obtained by increasing n to 4. The degree of purification from impurity of metals such as Pb, Ag, Zn, Cu, Fe and the morphology of the bismuth (III) oxalates were also determined. The maximum degree of the removal of the impurities is shown to achieved by the precipitation of Bi-2(C2O4)(3)center dot 8H(2)O as the desired product from industrial bismuth nitrate solutions. Bismuth oxalates with compositions Bi(C2O4)OH and Bi-2(C2O4)(3)center dot 7H(2)O are the fine-grained powders, which could be used as precursors for the synthesis of the bismuth oxide materials.