Precipitation Process for Zr-Bearing Waste Acid

Sodium fluoride is vised as the precipitant for removing Zr from the HF-HNO3 solution as zlrconate salt at the point of generation. The precipitation reaction is shown in Equation (1)  

The waste acid used for the tests with Zr was the effluent from etching operations. The acid concentrations averaged 22 g/L HF and 400 g/L HNO3 with the Zr concentration averaging 45 g/L. Minor metal impurities in solution included Al, Be, Cr, Cu, Fe, 

and Si, which typically had concentrations of 0.1 g/L. The test conditions that were varied included reaction temperature, impeller tip speed during reaction and crystallization, stoichiometry, and length of reaction and crystallization periods. The test conditions were varied as listed below and were based on information in the literature (Megy and Propst 1978)  

Reaction Temperature Impeller Tip Speed Stoichiometry Reaction Time Crystallization Time NaF Addition 

Data collected for each run included acid analysis using inductively coupled plasma (ICF) to determine cation concentration and titration to determine H concentration. Filtering characteristics were determined using solid and filtrate yield rates, as well as back pressures during the filtration cycle. The filter cake was characterized by moisture content and composition. Solid samples were analyzed with scanning electron microscopy (SEM) to determine changes in particle shape and size under various process conditions, and X-ray diffraction (XRD) was used to determine the solids composition. 

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