Simultaneous removal of Pb2 +, Cu2 +, Zn2 + and Cd2 + from highly acidic solutions using mechanochemically synthesized montmorillonite–kaolinite/TiO2 composite

• Composites of raw clay with amorphous and crystalline TiO2 were prepared by milling.
• Simultaneous adsorption of heavy metals on synthesized composites was investigated.
• The prominent improvement of sorption ability is achieved in acid solutions (pH < 4).
• The optimum amount of TiO2 in the composites is 20%.
• Difference in adsorption behavior lies in different crystalline forms of used TiO2.

The aim of the present study was to synthesize a composite of raw interstratified montmorillonite–kaolinite clay (Mt–K) with TiO2 as an additive by mechanochemical activation and investigate its usability as low-cost adsorbent for simultaneous removal of heavy metals from acidic aqueous solutions. The composite synthesized with amorphous TiO2 (TiO2,a) showed a significantly better removal ability of heavy metals from highly acidic solutions (pH = 2.0–4.0) compared with the Mt–K milled for an optimum period of time of 19 h (Mt–K,m) and composite synthesized with crystalline TiO2 (TiO2,c). As both of the composites showed the same morphologies, the same distribution of TiO2 particles on the clay matrix, the same particle size distribution (PSD) dependencies and point of zero charge (pHPZC) values, it has to be noticed that the difference in the adsorption behavior lies only in the different crystalline forms of the additive, i.e. TiO2 that was used for the composite preparation. It has been shown that 20% of TiO2,a was the optimal amount of an additive in the composite to achieve improved adsorption ability.