Wet Treatment Of Arsenic Caustic Sludge Preparation Of Colloidal Antimony Pentoxide

Arsenic-alkali residue, being dangerous to the environment, is a solid waste of antimony production by pyrometallurgy. So it's of very importance to treat and utilize arsenic-alkali residue comprehensively, which can both eliminate the environmental pollution and recycle the resource of arsenic and antimony, with high social and economic benefits. In this dissertation, a novel hydrometallurgical process was developed to prepare colloidal pentoxide antimony using arsenic-alkali residue as raw material, including water leaching, acid leaching, hydrolyzing and preparing colloidal Sb₂O₅ 。Water leaching is effective to separate arsenic from antimony. arsenic is dissolved in the solution and antimony still exists in the residue with water leaching. According to the orthogonal and single factor experiment, the optimized conditions which the leaching rate of arsenic is over 99% and remained rate of antimony is about 4% were obtained, i.e., the ratio of liquid and solid being 6/1, temperature being 40℃ and reaction-time being 40 min.The water leached residue was leached by acid. HC1 being substituted by mixed HCl-H₂SO₄ solution , the leaching rate of antimony was increased ,with the temperature and the ratio of liquid to solid reduced. When the conditions were controlled to be at a temperature of 60℃, leaching time of 45 min, ratio of liquid to solid 8:1, and the volume ratio of HC1 to H₂SO₄ 5:1, the leaching rate of antimony is over 95%. The kinetics for leaching Sb³⁺ by HC1 is agreed with chemical reaction model. The passive films on the surface of water-leached residue, however,were destroyed by mixed acid, the reaction between Sb⁵⁺ and Sb was accelerated,resulted in leaching rate of antimonhy being increased.Under the conditions of the volume ratio of water to acid leachate being 2 : 1, room temperature, the transfer rate of antimony,Sb³⁺ and Sb⁵⁺ by hydrolysis are about 70.5%,62.5% and 86.7% respectively, and most impurities were removed with the solution being hydrolyzed for 1 hour.The stable colloidal antimony pentoxide was prepared by oxidationof the mixture of Sb2O3 and Sb2O5 obtained from arsenic-alkali residue by a hydrometallurgical process, with hydrogen peroxide being oxidant and phosphoric acid being stabilizer. Effects of main factors including aging time of the mixture, amount of phosphoric acid, the concentration of the mixture and the reaction temperature on the process of colloid formation and colloidal particle size were investigated in detail. The theories on thermodynamics, kinetics and electrical double layer (EDL) were used to analyze the experimental phenomena and results. It was concluded that no aging time was the most beneficial to form colloid, when molar ratio of phosphoric acid to antimony was in the range from 0.8 to 1.0 and 1.0 to 1.3, the particle sizes of sol with the concentration of 10 % and 15 % antimony pentoxide by weight are both smaller, and with the molar ratio of 1.0, the average particle sizes are (36±5.6)nm nm and (164±32)nm respectively. With increasing the concentration of the mixture of antimony oxide from 10 % to 20 %, the reaction time decreases from 90 min to about 30 min, but the optimized range of molar ratio of H3PO4 to antimony increases. The reaction temperature is not the main factor on particle size with the existence of H3PO4, the average particle size is c.a. 160nm without obviously variety in the temperature range from 60 °C to 90°C.The TEM patterns of colloidal particles show that particles are spherical shape needle and sheet shape. The process of Phase Transformation is heterogeneous nucleation.