The efficiency of sodium hydroxide treated rubber (Hevea brasiliensis) leaves powder (NHBL) for removing copper ions from aqueous solutions has been investigated. The effects of physicochemical parameters on biosorption capacities such as stirring speed, pH, biosorbent dose, initial concentrations of copper, and ionic strength were studied. The biosorption capacities of NHBL increased with increase in pH, stirring speed and copper concentration but decreased with increase in biosorbent dose and ionic strength. The isotherm study indicated that NHBL fitted well with Langmuir model compared to Freundlich and Dubinin-Radushkevich models. The maximum biosorption capacity determined from Langmuir isotherm was 14.97 mg/g at 27 degrees C. The kinetic study revealed that pseudosecond order model fitted well the kinetic data, while Boyd kinetic model indicated that film diffusion was the main rate determining step in biosorption process. Based on surface area analysis, NHBL has low surface area and categorized as macroporous. Fourier transform infrared (FT-IR) analyses revealed that hydroxyl, carboxyl, and amino are the main functional groups involved in the binding of copper ions. Complexation was one of the main mechanisms for the removal of copper ions as indicated by FT-IR spectra. Ion exchange was another possible mechanism since the ratio of adsorbed cations (Cu2+ and H+) to the released cations (Na+, Ca2+, and Mg2+) from NHBL was almost unity. Copper ions bound on NHBL were able to be desorbed at > 99% using 0.05 mol/L HCl, 0.01 mol/L HNO3, and 0.01 mol/L EDTA solutions.
The application of low-cost adsorbents obtained from plant wastes as a replacement for costly conventional methods of removing heavy metal ions from wastewater has been reviewed. It is well known that cellulosic waste materials can be obtained and employed as cheap adsorbents and their performance to remove heavy metal ions can be affected upon chemical treatment. In general, chemically modified plant wastes exhibit higher adsorption capacities than unmodified forms. Numerous chemicals have been used for modifications which include mineral and organic acids, bases, oxidizing agent, organic compounds, etc. In this review, an extensive list of plant wastes as adsorbents including rice husks, spent grain, sawdust, sugarcane bagasse, fruit wastes, weeds and others has been compiled. Some of the treated adsorbents show good adsorption capacities for Cd, Cu, Pb, Zn and Ni.
The adsorption of Cu(II) ions from aqueous solution by chitosan and chitosan/PVA beads was studied in a batch adsorption system. Chitosan solution was blended with poly(vinyl alcohol) (PVA) in order to obtain sorbents that are insoluble in aqueous acidic and basic solution. The adsorption capacities and rates of Cu(II) ions onto chitosan and chitosan/PVA beads were evaluated. The Langmuir, Freundlich and BET adsorption models were applied to describe the isotherms and isotherm constants. Adsorption isothermal data could be well interpreted by the Langmuir model. The kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step. The Cu(II) ions can be removed from the chitosan and chitosan/PVA beads rapidly by treatment with an aqueous EDTA solution. Results also showed that chitosan and chitosan/PVA beads are favourable adsorbers.
The adsorption of humic acid on crosslinked chitosan-epichlorohydrin (chitosan-ECH) beads was investigated. Chitosan-ECH beads were characterized by Fourier transform infrared spectroscopy (FTIR), surface area and pore size analyses, and scanning electron microscopy (SEM). Batch adsorption experiments were carried out and optimum humic acid adsorption on chitosan-ECH beads occurred at pH 6.0, agitation rate of 300 rpm and contact time of 50 min. Adsorption equilibrium isotherms were analyzed by Langmuir and Freundlich models. Freundlich model was found to show the best fit for experimental data while the maximum adsorption capacity determined from Langmuir model was 44.84 mg g(-1). The adsorption of humic acid on chitosan-ECH beads was best described with pseudo-first-order kinetic model. For desorption study, more than 60% of humic acid could be desorbed from the adsorbent using 1.0M HCl for 180 min.
In this study, iron impregnated activated carbon (FeAC) was synthesized following an oxidation and iron impregnation of activated carbon (AC). Both the AC and FeAC were characterized by pHZPC and FTIR spectroscopy. The removal of Methylene Blue (MB) by AC and FeAC was examined under various experimental conditions. The FeAC showed up to 95% (higher than AC) MB removal in the pH range of 7-10. Although the reaction kinetics was pseudo-second order, the overall rate was controlled by a number of processes such as film diffusion, pore diffusion and intraparticle diffusion. The activation energy values for the MB uptake by AC and FeAC (21.79 and 14.82 kJ/mol, respectively) revealed a physisorption process. In the regeneration study, FeAC has shown consistently ≥ 90% MB removal even up to 10 repeated cycles. The reusable characteristic of the spent FeAC improved the practical use of activated carbon and can be a breakthrough for continuous flow system applications where it can work effectively without any significant reduction in its performance.
Bioregeneration of mono-amine modified silica gel (MAMS) adsorbent loaded with Acid Orange 7 (AO7), Acid Yellow 9 (AY9) and Acid Red 14 (AR14), respectively, was investigated under two different operational conditions, namely absence/presence of sucrose/bacto-peptone as the co-substrate and different biomass acclimation concentrations. The results revealed that the AY9- and AR14-loaded MAMS adsorbents could almost be completely bioregenerated but only in the presence of co-substrate whereas the bioregeneration of AO7-loaded MAMS could achieve up to 71% in the absence of the co-substrate. These differences could be related to the structural properties of the investigated azo dyes. In addition, the results showed that the bioregeneration duration of AO7-loaded MAMS could be progressively shortened by using biomass acclimated to increasingly higher AO7 concentration. However, the bioregeneration efficiencies were found to be relatively unchanged under different biomass acclimation concentrations.