Surface modifications of talcs. Effects of inorganic and organic acid treatments

A multipurpose acid treatment, which comprises purification, delamination, particle size reduction, and surface modification on milled talc samples, is proposed. Talcs of different origins and composition were studied in order to assess and compare the effects of different acid treatments. Associated minerals were dissolved away by both inorganic and monocarboxylic organic acids, rendering more pure and lower particle size talcs. The main results obtained from hydrochloric acid treatment were purified talcs, having silanol groups onto their surfaces. This treatment allowed the complete removal of carbonates and chlorite from initial talcs, allowing for a length and thickness reduction of talc particles and the change to hydrophilic character by breakage of siloxane bonds. The so-treated talc achieved a purity level enough to be used in plastic and paper industry, paints among other upgraded talc applications. On the other hand, organic acid attacks were able to graft carboxylic groups onto the talc surface. The occurrence of this reaction was verified by independent characterization techniques both direct (Fourier Transform Infrared Spectroscopy, Energy Dispersive X-ray) and indirect (X-ray Diffraction, Scanning Electronic Microscopy, hydrophobicity/hydrophilicity test).