Z. Reddad

Modeling the adsorption of metal ions (Cu2+, Ni2+, Pb2+) onto ACCs using surface complexation models

Activated carbon cloths (ACCs), whose efficiency has been demonstrated for microorganics adsorption from water, were here studied in the removal of metal ions from aqueous solution. Two ACCs are investigated, they are characterized in terms of porosity parameters (BET specific surface area, percentage of microporosity) and chemical characteristics (acidic surface groups, acidity constants, point of zero charge). A first part consists in the experimental study of three metal ions removal (Cu2+, Ni2+ and Pb2+) in a batch reactor. Isotherms modeling by Freundlich and Brunauer–Emmett–Teller (BET) equations enables the following adsorption order: Cu2+>Ni2+>Pb2+ to be determined for adsorption capacities on a molar basis. It may be related to adsorbates characteristics in terms of electronegativity and ionic radius. The influence of adsorbent’s microporosity is also shown. Adsorption experiments carried out for pH values ranging from 2 to 10 demonstrate: (i) an adsorption occurring below the precipitation pH; (ii) the strong influence of pH, with a decrease of electrostatic repulsion due to the formation of less charged hydrolyzed species coupled with a decrease of activated carbon surface charge as pH increases. The second part focuses on the modeling of adsorption versus the pH experimental data by the diffuse layer model (DLM) using Fiteql software. The model is efficient to describe the system behavior in the pH range considered. Regarding complexation constants, they show the following affinity for ACC: Pb2+>Cu2+>Ni2+. They are related to initial concentrations used for the three metal ions.

Cadmium and lead adsorption by a natural polysaccharide in MF membrane reactor: experimental analysis and modelling

In the present work, Pb(2+) and Cd(2+) adsorption onto a natural polysaccharide has been studied in membrane reactors. The process involves a stirred semi-batch reactor for the adsorption step and a microfiltration (MF) process in order to confine the particles. Due to their lower affinity for the biosorbent, Cd(2+) ions were found to breakthrough the process faster than Pb(2+) cations. The experimental results showed the technical feasibility of the pilot. A mass balance model based on the Langmuir equilibrium isotherm was used to describe the adsorption process. This relation is able to predict experimental data under different operating conditions: the adsorbent and metal concentrations, and the permeate flow rate. Based on these results, it is demonstrated that the biosorbent studied represents an interesting low-cost solution for the treatment of metal ions polluted waters.

Mechanisms of Cr(III) and Cr(VI) removal from aqueous solutions by sugar beet pulp

Abstract The removal of three‐ and hexavalent chromium from aqueous solutions using sugar beet pulp as biosorbent substrate was performed. The kinetics of Cr(III) and Cr(VI) removal were studied at 20.0 ± 0.5 °C and under various experimental conditions. The Cr(III) ions were adsorbed onto the biosorbent by ion‐exchange mechanism with Ca2+ cations. The influence of solution pH was found to greatly affect the adsorption efficiency of Cr(VI). Cr(VI) removal was largely involved in a reduction mechanism with the appearance of Cn(III) ions in the solution.

Competitive adsorption of metals and organics onto a low cost natural polysaccharide

Abstract Metals removal onto a low‐cost natural polysaccharide is performed. Firstly, some specific characteristics of adsorbent are determined. Potentiometric titrations of the sorbent have been realised. The values of the point of zero net proton charge (pznpc) and the cation exchange capacity (CEC) deduced from these experiments have given respectively pH=5 and 0.575 meq g‐1. Secondly, Sorption of cations from single metallic solution, have been performed and the equilibrium fixation capacities are 0.37 mmol g‐1 for Pb2+, 0.28 mmol g‐1 for Cu2+ and 0.2 mmol g‐1 for Ni2+. In multi‐metals solutions of equimolar concentration, Ni2+ ions present the greatest fixation decrease in the presence of the two other cations (‐ 61 %), Pb2+ and Cu2+ seem to compete similarly. In the presence of a constant organic load composed of either benzaldehyde, benzoic acid or phenol and expressed as 100 mg 1‐1 total organic carbon (TOC), benzoic acid induces the largest reduction of the copper equilibrium fixation capacity (‐ 30 %).