Removal of malachite green (MG) from aqueous solutions by adsorption, precipitation, and alkaline fading using talc: kinetic, thermodynamic, and column feasibility studies

Abstract

Malachite green (MG) has been widely used in the dyeing industry and as a fungicide and an antiseptic in the aquaculture industry. However, MG is very dangerous and cytotoxic to mammalian cells, and its discharge into receiving waters results in environmental problems in aquatic ecosystems. To remove this soluble dye from aqueous solutions, adsorption by inorganic clay is often used. In the case of the triphenylmethane dye family, molecular structure changes occur with changes in pH. As a result, chromatic MG(+) at a neutral pH turns into the protonated MG (MGH(2+)) at an acidic pH and into the carbinol base form at a basic pH. In this study, taking into consideration the potential for MG structural change, batch sorption experiments for kinetics (5-1.17, 10-2.94, and 20-5.90 MG mg/mL at 293, 303, and 313K) and thermodynamics (calculated activation energy (E-a)=2.09kJ/mol) as well as tests of the feasibility of column flushing were conducted using talc to remove MG from aqueous solutions (100% removal after 140 pore volumes of a 12-h run). We studied specific removal behaviors of MG by talc for pH values>8.0, where MG molecules that had adsorbed onto the talc predominantly changed to the carbinol base form and were retained on the talc.