Neutralization of Acidic Wastewater by the Use of Waste Limestone from the Marble Industry. Mechanistic Aspects and Mass Transfer Phenomena of the Acid−Base Reaction at the Liquid−Solid Interface

Waste limestone from marble cutting operations was adopted as a neutralizing agent of acidic wastewater from the glass industry. Hydrogen fluoride containing wastewater from the glass matting operations was investigated with the final aim of studying the influence of mass-transfer phenomena at the liquid−solid interface of the heterogeneous neutralization reaction as the rate determining step of the overall process. In this context, chemicals interdiffusion at the stationary liquid film (Nernst film) around the particles and/or in the particles themselves may play a relevant role as kinetic rate determining step. Specifically, the influence of the stirring speed, temperature of the liquid−solid mixture, and grain size of the limestone particles during batch neutralization operations were analyzed in order to carry-out a mechanistic study of the acid−base reaction at the liquid−solid interface. Apparently, limestone is not the best material to be used in the neutralization of HF containing wastewater because of molecular interdiffusion hindrances of the involved species. The present work is essentially aimed to the interpretation of mechanistic aspects of the neutralization reaction in the reference heterogeneous solid−liquid system.