Arsenic removal from water/wastewater using adsorbents—A critical review

https://www.jpcomplex.ir/Content/media/image/2013/08/772_orig.pdf

Electrochemical technologies in wastewater treatment

Heavy metal removal from water/wastewater by nanosized metal oxides: a review.

The article focuses on adsorption of heavy metal ions on soils and soils constituents such as clay minerals, metal (hydr)oxides, and soil organic matter. Empirical and mechanistic model approaches for heavy metal adsorption and parameter determination in such models have been reviewed. Sorption mechanisms in soils, the influence of surface functional groups and surface complexation as well as parameters influencing adsorption are discussed. The individual adsorption behavior of Cd, Cr, Pb, Cu, Mn, Zn and Co on soils and soil constituents is reviewed.

Adsorption of heavy metal ions on soils and soils constituents

The characterization of activated carbons with oxygen and nitrogen surface groups

Cadmium adsorption isotherms were conducted using two commercially available powdered activated carbons (PACs). Isotherms were conducted at several pH values and metal and carbon concentrations. Both PACs removed significant amounts of cadmium, and removal was a strong function of solution pH: increasing the solution pH increased cadmium adsorption. Adsorption data at a specific pH were successfully modeled using both the Langmuir and Freundlich isotherms. Adsorption and surface precipitation were hypothesized to be the operative removal mechanisms. Cadmium removal is strongly related to the carbon's pHzpc, acid-base characteristics, and surface charge-pH relationship. Surface area, an important adsorption parameter for organic adsorbates, does not appear to influence metal removal strongly.

Modeling cadmium adsorption by activated carbon using the langmuir and freundlich isotherm expressions

The removal of As(III), As(V), Hg(II), and Pb(II) by virgin and Fe(III) impregnated activated carbons (FeAC) was investigated. Iron-oxide impregnation increased the pHzpc of the carbon from 7.5 to about 8.2–8.7 but did not alter the surface area or the pore volume. The amount of acid or base needed to reach a given pH increased following impregnation, indicating that the FeAC was more active than its non-impregnated counterpart. Metal removal was a function of pH with removal increasing with pH for Hg(II) and Pb(II) and decreasing with pH for As(V). As(III) removal was not a strong function of pH below pH = 5, increased to a maximum at pH ≈ 7, then decreased with increasing pH. As(III) and As(V) removals were about one and two orders of magnitude higher, respectively, for the FeAC compared with the non-impregnated carbon, while Hg(II) and Pb(II) removals were only slightly higher. Fe-impregnation appears to be most effective for the anionic contaminants.

As(III), As(V), Hg, and Pb Removal by Fe-Oxide Impregnated Activated Carbon

A contaminated, iron oxide coated (15.5% Fe 2 O 3 ), sandy soil was studied to evaluate the effectiveness of conventional soil-washing extractants for metal removal. Metals of interest included As, Cu, Pb, Hg, and Zn. The extractant solutions were HCl, HNO 3 , H 2 SO 4 , EDTA and NH 2 OH.HCl. Experiments assessed erects of extractant strength and contact time. Individual soil size fractions were studied for the various extractants. Metal-binding mechanisms were evaluated using a sequential extraction procedure. Metals in all size classes were bound strongly, presumably by an Fe oxide coating observed on the sandy soil. From an analysis of particle size fractions, contaminated soil metal concentration correlated approximately with the surface area/volume ratio of soil particles, suggesting that the metals were associated with soil surfaces

Metal removal by soil washing for an iron oxide coated sandy soil

Cadmium and nickel adsorption isotherms were performed using three activated carbons in ligand-free systems and in the presence of EDTA, succinic acid, PO4 (Ni only), NH4BF4 (Cd only), competing metals (Ni and Cd), and differing ionic strengths and background electrolytes. Generally, all carbons removed metals from the ligand-free systems. Four scenarios were forwarded which described metal adsorption in the presence of various organic and inorganic compounds. The effect of organic and inorganic ligands on metal removal was dependent on the carbon, metal, and ligand type and concentration. The presence of a second heavy metal did not affect removal of the primary metal ion. Increasing ionic strength decreased metal removal for all carbons and metals investigated while the type of background electrolyte had no effect on metal removal.

Metal Adsorption by Activated Carbon: Effect of Complexing Ligands, Competing Adsorbates, Ionic Strength, and Background Electrolyte

The in-situ remediation of a lead-contaminated soil (silt loam, K H = 5 × 10 −8 cm/s, soil Pb = 1,000 mg/kg) by electrokinetic (EK) soil flushing [60 V (DC)] was studied. Research focused on the chemical conditioning of the electrode reservoirs with either 500 μS/cm (as NaNO 3 , baseline behavior), acetic acid (HAc), HCl, or EDTA. For baseline tests there were significant amounts of lead transported through the soil, but the Pb precipitated or was readsorbed on the soil adjacent to the cathode because of the high soil pH in that region. The addition of 1 M HAc to the cathode reservoir prevented the formation of the basic conditions in the soil, and about 65% of the Pb was transported into the cathode. When HCl was added to the anode and HAc was added to the cathode, more than 75% of the lead resided in the cathode. Pb removals in the EDTA experiments were greater than those observed in the baseline experiments and were similar to those observed in the HCl-HAc experiments. A low anode reservoir pH resultin...

Brian E. Reed

Papers

Modeling cadmium adsorption by activated carbon using the langmuir and freundlich isotherm expressions

As(III), As(V), Hg, and Pb Removal by Fe-Oxide Impregnated Activated Carbon

Metal removal by soil washing for an iron oxide coated sandy soil

Metal Adsorption by Activated Carbon: Effect of Complexing Ligands, Competing Adsorbates, Ionic Strength, and Background Electrolyte

Chemical Conditioning of Electrode Reservoirs During Electrokinetic Soil Flushing of Pb-Contaminated Silt Loam