Natural zeolites as effective adsorbents in water and wastewater treatment

Physico-chemical treatment techniques for wastewater laden with heavy metals

Humic acid (HA) coated Fe3O4 nanciparticles (Fe3O4/HA) were developed for the removal of toxic Hg(II), Pb(II), Cd(II), and Cu(II) from water. Fe3O4/HA were prepared by a coprecipitation procedure with cheap and environmentally friendly iron salts and HA. TOC and XPS analysis showed the as-prepared Fe3O4/ HA contains similar to 11% (w/w) of HA which are fractions abundant in O and N-based functional groups. TEM images and laser particle size analysis revealed the Fe3O4/HA (with similar to 10 nm Fe3O4 cores) aggregated in aqueous suspensions to form aggregates with an average hydrodynamic size of similar to 140 nm. With a saturation magnetization of 79.6 emu/g, the Fe3O4/HA can be simply recovered from water with magnetic separations at low magnetic field gradients within a few minutes. Sorption of the heavy metals to Fe3O4/HA reached equilibrium in less than 15 min, and agreed well to the Langmuir adsorption model with maximum adsorption capacities from 46.3 to 97.7 mg/g. The Fe3O4/HA was stable in tap water, natural waters, and acidic/ basic solutions ranging from 0.1 M HCl to 2 M NaOH with low leaching of Fe (<= 3.7%) and HA (<= 5.3%). The Fe3O4/HA was able to remove over 99% of Hg(II) and Pb(II) and over 95% of COO and Cd(II) in natural and tap water at optimized pH. Leaching back of the Fe3O4/HA sorbed heavy metals in water was found to be negligible.

Coating Fe3O4 Magnetic Nanoparticles with Humic Acid for High Efficient Removal of Heavy Metals in Water

Heavy metals like arsenic, copper, cadmium, chromium, nickel, zinc, lead, and mercury are major pollutants of fresh water reservoirs because of their toxic, non-biodegradable, and persistent nature. The industrial growth is the major source of heavy metals introducing such pollutants into different segments of the environment including air, water, soil, and biosphere. Heavy metals are easily absorbed by fishes and vegetables due to their high solubility in the aquatic environments. Hence, they may accumulate in the human body by means of the food chain. Various methods have been developed and used for water and wastewater treatment to decrease heavy metal concentrations. These technologies include membrane filtration, ion-exchange, adsorption, chemical precipitation, nanotechnology treatments, electrochemical and advanced oxidation processes. In this review, the methods as well as their mechanisms and efficiency are discussed.

Removal of Heavy Metals from Industrial Wastewaters: A Review

Kinetics of adsorption of metal ions on inorganic materials: A review

In this study, we investigated the removal of Fe, Pb, Cd, and Zn from synthetic mine waters by a natural zeolite. The emphasis was given to the zeolite's behavior toward a few cations in competition with each other. Pb was removed efficiently from neutral as well as from acidic solutions, whereas the uptake of Zn and Cd decreased with low pH and high iron concentrations. With increasing Ca concentrations in solution, elimination of Zn and Cd became poorer while removal of Pb remained virtually unchanged. The zeolite was stable in acidic solutions. Disintegration was only observed below pH 2.0. Forward- and back-titration of synthetic acidic mine water were carried out in the presence and absence of zeolite to simulate the effects of a pH increase by addition of neutralizing agents and a re-acidification which can be caused by subsequent mixing with acidic water. The pH increase during neutralization causes precipitation of hydrous ferric oxides and decreased dissolved metal concentrations. Zeolite addition further diminished Pb concentrations but did not have an effect on Zn and Cd concentrations in solution. During re-acidification of the solution, remobilization of Pb was weaker in the presence than in the absence of zeolite. No substantial differences were observed for Fe, Cd, and Zn immobilization. The immobilization of the metals during pH increase and the subsequent remobilization caused by re-acidification can be well described by a geochemical equilibrium speciation model that accounts for metal complexation at hydrous ferric oxides, for ion exchange on the zeolite surfaces, as well as for dissolution and precipitation processes.

Removal of Heavy Metals from Mine Waters by Natural Zeolites

Sorption of antimonate by HDTMA-modified zeolite

Adsorption of Pb and Cd by amine-modified zeolite.

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Removal of Heavy Metals from Mine Waters by Natural Zeolites

Sorption of antimonate by HDTMA-modified zeolite

Adsorption of Pb and Cd by amine-modified zeolite.