Reactive Red 120 Dye Removal from Water Systems Using Natural Minerals: Batch Adsorption Approach

The study investigated the adsorption capacity of natural minerals such as limestone sand (LS), silica spongolite (SS), chalcedonite (CH), and dolomite (DO) for the removal of a model contaminant, the azo dye Reactive Red 120 (RR-120). The effects of adsorbent dose and solution pH on adsorption, as well as the adsorption kinetics and equilibrium adsorption, were investigated. The results showed that adsorption was dependent on the mass of the adsorbent and increased with increasing adsorbent dose. Adsorption was also dependent on the pH of the initial solution and was most efficient in an acidic media. Adsorption kinetic research results revealed that the adsorption of RR-120 on all four minerals followed the pseudo-second-order model and was controlled by film diffusion. The dye adsorbed fastest on limestone sand (k(2 )= 0.021 g/mu mol center dot min) and slowest on dolomite (k(2) = 0.015 g/mu mol center dot min). The observed adsorption rate increases in the order of DO < CH < SS < LS. Under equilibrium conditions, Reactive Red 120 was adsorbed best on dolomite and least on limestone sand (LS < SS < CH < DO). The Langmuir adsorption capacities for RR-120 were found to be 4.7 mu mol/g for LS, 5.2 mu mol/g for SS, 7.0 mu mol/g for CH, and 9.0 mu mol/g for DO. The results indicate that selected natural minerals can be employed as alternatives to commercial adsorbents for the removal of Reactive Red 120 from water.