Dissolution of bentonite and release of rare earth elements at different solid / liquid ratios in a simulated wine purification process

Abstract

The extraction of rare earth elements (REE) from bentonite was studied in a simulated process of purification of wine using a tartaric acid solution and white wine (Rhine Riesling). Two types of commercially available bentonite were used: gelbentonite and superbenton. The rate of dissolution was determined on the basis of batch experiments. Laboratory experiments corresponding to winemaking technology demonstrated that the process attains maximum velocity in the first 48 h, during which Al and Si are released into solution. No significant changes in the pH were observed (from 3.2 to 3.4) during the interactions of wine and tartaric acid with both bentonites; in this pH range, the surface reactions probably occur mainly on negatively charged basal planes. The rate of dissolution of bentonite varied in the range 10−10.46 M Si s−1 m−2 to 10−12.51 M Al s−1 m−2. The rate of dissolution and Al/Si stoichiometry in the extracts of both bentonites are higher for extraction with tartaric acid. REE contained in the extracts correspond both to the desorption process and also to dissolution of the bentonite itself, especially in cases of faster extraction with tartaric acid. The relative amount of mobilized REE, expressed in the form of Kd, decreases with increasing S/L ratio. Desorption is accompanied by fractionation of REE, and HREE are preferentially extracted into solution. The fractionation of REE is not apparent during dissolution of bentonite. As up to 7.5% of the bentonite is dissolved in extraction with tartaric acid, the REE contents firmly bonded in the lattice structures of the individual silicates also affect the compositions of the extracts.