Removal of heavy metals from wastewater with natural and modified sorbents

The paper presents research results of heavy metal ions sorption from a model solution and wastewater of an electroplating enterprise under static conditions. The purpose of this work is to develop a technology of tertiary treatment of electroplating production wastewater from heavy metals to achieve MPC levels for fresh fishery water bodies using local powder sorption materials. The authors examined such sorbents as modified clay (MC) obtained by thermal modification of its natural components (montmorillonite, kaolinite, peat, dolomite), as well as certain primary components and their mixtures without thermal modification. The studies were conducted at low initial concentrations of heavy metals (from 0.002 to 2.8 mg/l) characteristic of wastewater subjected to tertiary treatment. The concentration of heavy metals in wastewater was determined by inductively coupled plasma optical emission spectrometry on Avio™ 200. The research demonstrated that the contact time required to achieve the equilibrium of the treated wastewater and the modified clay sorbent varied from 60 to 120 minutes for the investigated heavy metals. Taking into account the time required to reach the MPCs of heavy metals for fresh fishery water bodies, the estimated contact duration of 90 minutes was recommended. The calculated dose of the modified clay sorbent, sufficient for tertiary treatment of acid-base wastewater of electroplating production to the MPC, was 1 g/l. Experiments with unmodified materials conducted on a multicomponent model solution showed that montmorillonite had the best sorption properties, ensuring the achievement of MPC for all metals, except aluminum, at doses from 0.1 to 0.9 g/l. Peat was the most effective in extracting nickel to MPC with its estimated dose being 0.1 g/l. Dolomite turned out to be the only material that provided the removal of aluminum to MPC at a dose of 1 g/l. The obtained results suggest that it is possible to increase the efficiency of heavy metals removal by selecting sorbent mixture without thermal modification and with mixed sorbent dose of 1–1.6 g/l. The authors recommend a technology of tertiary treatment of acid-base wastewater of electroplating production. This technology is to carry out the sorption process under static conditions using powder sorbents based on local natural materials, followed by separation of the spent sorbent with a precoat cartridge filter.