Zeitschrift für Chemieingenieurwesen und Prozesstechnologie
Offener Zugang

Abstrakt

The Effect of Temperature and Pressure on the separation of Calcium Carbonate and Barium Sulphate from a Mixed Sludge

Rukuni TT, Maree JP, Zvinowanda CM and Carlsson FHH

South Africa is one of the first countries to implement full-scale mine water reclamation to drinking water quality. Reverse osmosis is already being used on full scale for desalination of mine water. However, with increased recycling of mine water, the result has been the increased generation of sludge. The Council for Scientific and Industrial Research (CSIR) has developed the Alkali-Barium-Carbonate (CSIR-ABC) process that can be used for neutralization and desalination of sulphate-rich effluents while recovering valuable by-products from the mixed sludge’s produced. A mixture of BaSO₄ and CaCO₃ sludge is produced as one of the by-products, which preferably needs to be separated into its components prior to thermal treatment. The aim of this study was to separate CaCO₃ and BaSO₄ from a CaCO₃-BaSO₄ mixed sludge through dissolution of CaCO₃ as Ca(HCO₃)₂ in contact with CO₂. Measured quantities of a simulated CaCO₃-BaSO₄ mixed sludge from the CSIR-ABC process were fed into a reactor vessel containing deionized water and pressurized CO₂ was introduced. The effects of temperature and pressure with time were investigated while monitoring alkalinity, pH and calcium concentration. The findings of this study were: (1) The dissolution rate of CaCO3 was rapid i.e. from 0 to 2000mg/L in the first 20minutes; (2) Ca(HCO₃)₂ had a high solubility of about 2600 mg/L when in contact with CO₂ at 1atm., while BaSO₄ was almost completely insoluble; (3) The solubility of Ca(HCO₃)₂ increased with decreasing temperature and increasing pressure; (4) CaCO₃, after conversion to Ca(HCO₃)₂, was separated from BaSO₄ in a CaCO₃-BaSO₄ mixed sludge; (5) Visual MINTEQ model is a powerful tool that can be used to predict the solubilities of CaCO₃ and BaSO₄ when contacted with CO₂.