A new adsorbent modified from orange peel (OP) was successfully synthesized by ethylenediamine crosslinking method to remove Cr(VI) from wastewater. The modified orange peel powder (MOPP) was investigated in a batch adsorption system, including both equilibrium adsorption isotherms and kinetics. Effects of several factors, including adsorbent dose, initial pH and Cr(VI) concentration were studied. The data indicated that the pH was not an essential factor that affected the adsorption process, it has a wide pH range from 4 to 10, and high adsorbent dose and lower Cr(VI) concentration could increase the Cr(VI) removal efficiency. Equilibrium data were analysed using the Langmuir, Freundlich and Temkin isotherm models and found to be well represented by the Langmuir isotherm model. The maximum capacity (qmax) obtained from Langmuir model was 52.08 mg/g at pH 6.0. The kinetics of adsorption followed the pseudo-second-order kinetic equation. The results suggest that MOPP is an inexpensive and efficient adsorbent for removing Cr(VI) from aqueous solution.

The paper deals with the feasibility of arsenite removal by the adsorption from bentonite mineral. Groundwater arsenic contamination has been reported in different parts of the world including Jharkhand, Bihar and Uttar Pradesh. Tube wells in Holocene Newer Alluvium are characterized by grey to black coloured organic-rich argillaceous sediments which have arsenic-contaminated groundwater. The majority of arsenic present in the groundwater is in the form of As(III) which exists as uncharged species arsenic tri hydroxide at pH value of less than 9.2. Arsenite is removed by various techniques like coagulation microfiltration, fixed bed adsorption, bioremoval, ion exchange, membrane filtration, etc. Our studies have shown that locally available bentonites containing a unit of montmorillonites can remove the arsenic from an aqueous medium. On the treatment of 100 mL arsenite solution with 300 mesh sieves bentonites up to different intervals of time, it has been found that bentonites are good adsorbent of arsenite. The percentage removal of arsenite is up to 99 per cent with 3 g sodium derivative of bentonite for 1 hour. The removal efficiency, adsorption isotherm and kinetic studies show the suitability of bentonite minerals for arsenic removal following first-order kinetics. Freundlich and Langmuir isotherms are obeyed in the adsorption of arsenite by bentonite minerals. Adsorption of arsenic by bentonite minerals has proved to be a low-cost eco-friendly method. Sodium derivative of bentonite minerals has been found more efficient for removal of arsenite.

Raw kaolinite clay collected from Ire-Ekiti, Ekiti State, Nigeria, was used to adsorb some heavy metals (Pb, Cr, Ni and Cu) from their aqueous solution through batch experiments. Adsorption studies were performed at the different temperatures, concentration and time to determine the kinetics, isotherm and thermodynamic properties of the adsorption processes. The adsorption thermodynamic properties showed that sorption of Cu, Cr and Ni on the raw clay was exothermic, while adsorption of Pb was endothermic. The negative values of ?G for Pb adsorption revealed the feasibility and spontaneity of the adsorption process while the positive ?G values for Cu, Cr and Ni sorption showed non-spontaneity of the adsorption process. Langmuir, Freundlich and Elovich isotherms were applied to explicate the nature of adsorption process, while Pseudo-first-order (PFO), Pseudo-second-order and Elovich kinetics were applied to literarily determine the adsorbate-adsorbent interaction. Pseudo-second-order kinetics was the best fitting kinetics for adsorption of the metals on the raw clay.

The study gives the elimination of two kinds of antibiotics, tetracycline (TC) and cefradine (CF) by adsorption process, on the biochar derived from cornstalk. Dense, multifaceted and thick fragments of raw cornstalk almost all vanished at a pyrolytic temperature above 400°C. The carbon content increased from 60.48% of the raw cornstalk to 75.5% of the cornstalk biochar pyrolyzed at 600°C (BC600), while the oxygen content decreased from 17.31% to 6.94%. The uptake of each TC and CF on the cornstalk biochar was highly pH-dependent. The maximum adsorption capacities of TC and CF at 298 K calculated from the Langmuir mannequin have been 28.0 and 38.0 mg/g, respectively. The Columbic interaction and ?–? electron-donor-acceptor interaction between cornstalk biochar and CF/TC molecules played the main role. The experimental records were well outfitted by way of the ability of the pseudo-second-order kinetics model, indicating a possible chemisorption process to some extent. Isotherm result implied that both adsorption and partitioning contributed to the uptake of TC and CF onto BC600.

The release of textile effluents into the biosphere is a serious threat to the environment and promotes several health issues. Although several studies have been carried out in the remediation of textile effluents using adsorbents, the continuous mode of operation (packed bed) to treat effluent generated from the cotton-based textile industry using biosorbent is seldom reported. Here, one such investigation is made to remediate the Remazol effluent solution in batch and continuous mode of operation. A maximum decolourization efficiency of 77.5% and 49.66% was obtained for Ulva lactuca derived biochar in batch and continuous study. Column data parameters such as overall sorption time zone, breakthrough time, exhaustion time and volume of effluent treated were also calculated. Regeneration studies showed that 0.01 M sodium hydroxide can be utilized for sorption-elution up to three regeneration cycles.

In this study, the adsorption performance of rice wine lees on reactive brilliant red (X-3B) was studied. Five aspects of SEM, FTIR characterization of rice wine lees, initial X-3B pH, rice wine lees dosage and initial dye concentration were studied. The characterization of rice wine lees indicated that it was a good adsorbent due to its larger specific surface area. And the experiment results showed that pH had a great influence on the adsorption effect of rice wine lees, and the adsorption performance decreased with the increase of pH. At the same time, the removal rate of reactive brilliant red X-3B increased with the increase of the dosage of rice wine lees and decreased with the increase of initial concentration of dyes. In the meanwhile, the experimental data were fitted to find that the adsorption of Reactive Brilliant Red X-3B by rice wine lees followed the Langmuir isotherm model. The adsorption kinetics was consistent with the intraparticle diffusion model and the maximum adsorption capacity was 12.376 mg/g.

Bentonite/chitosan composite was synthesized and characterized by different techniques including XRD, FT-IR, SEM and TEM to detect its physicochemical properties. The composite was introduced in realistic purification application to reduce the dissolved iron content in raw groundwater sample by fixed-bed column system. The plotted breakthrough curves and the related mathematical parameters revealed that the column achieves iron removal percentage of about 69% from 6.6 L of water after adjusting the factors affecting the system at 3 cm bed thickness, 5 mL/min flow rate, 5 mg/L concentration and pH 6. Applying the column system to remove iron from groundwater under the same conditions can achieve iron removal percentage of about 69% from a total volume of 8.2 L of water. The interaction of the metal on the column was attained after 18 hours and the saturation time was attained after 27.5 hours which revealed the high performance of the composite in the designed column system for the purification of groundwater.