Isotherm and selectivity studies of Ni(II) removal using natural and acid-activated nanobentonites

In this research, natural bentonite and its acid-activated forms were employed as adsorbents for the adsorption of Ni2+ ions from wastewater. Natural bentonite was activated with 2M sulfuric acid, 4.5 h and 95 °C (the beast acid-activated sample with the highest adsorption capacity) and the other 6M sulfuric acid, 7.5 h and 95 °C (the worst acid-activated sample with the lowest adsorption capacity). The adsorption of Ni2+ was studied through experiments including equilibrium contact time and selectivity. The equilibrium time of contact for bentonite was obtained at 180 min. The Ni2+ separation process along with Zn2+ selectivity studies was considered through adsorption experiments. The results showed that there was a maximum amount of Ni2+ adsorption in the absence of Zn2+ for all samples. The results showed the best fit is obtained with the pseudo-second-order kinetic model. Working out different bentonite types to determine the best kinetic models, we explored the Langmuir and Florry–Huggins models provided a good fit with experimental data for acid-activated bentonites and the best results from linear forms of the adsorption isotherm models for fitting the experimental data of natural bentonite are obtained Langmuir, Temkin and Freundlich models.

Batch Adsorption Assessment of Neem Nut Carbon for Abating Chromium(VI) in Wastewater

Discharge of Cr(VI) laden effluents is highly toxic and decontaminating the wastewater from Cr(VI) is necessary for Environmental Protection. An investigation on the adsorption characteristics of activated carbon prepared from neem nut (NNC) for the removal of Cr(VI) from wastewater by varying the parameters such as carbon dose, pH, equilibration time by batch studies was found to be effective for the removal of Cr(VI) from wastewater. Carbon characteristics of activated neem nut carbon were ascertained. Evaluation were done by varying the pH from 1 to 6, carbon dose from 0.1 g to 0.5 g and equilibration time from 1 to 6 hours. Maximum Cr(VI) removal of 95% took place when batch studies were done at an optimal pH of 2, carbon dose of 0.2 g//100mL, and equilibration time of 4 hours. Freundlich and Langmuir adsorption isotherm models were considered for analysis.

Adsorptive Removal of Arsenic and Lead by Stone Powder/Chitosan/Maghemite Composite Beads

Arsenic (As) and lead (Pb) contamination in groundwater is a serious problem in countries that use groundwater as drinking water. In this study, composite beads, called SCM beads, synthesized using stone powder (SP), chitosan (Ch), and maghemite (Mag) with different weight ratios (1/1/0.1, 1/1/0.3, and 1/1/0.5 for SP/Ch/Mag) were prepared, characterized and used as adsorbents for the removal of As and Pb from artificially contaminated water samples. Adsorption isotherm experiments of As and Pb onto the beads were conducted and single-solute adsorption isotherm models such as the Langmuir, Freundlich, Dubinin–Radushkevich (DR), and dual mode (DM) models were fitted to the experimental data to analyze the adsorption characteristics. The maximum adsorption capacities of the SCM beads were 75.7 and 232.8 mmol/kg for As and Pb, respectively, which were 40 and 5.6 times higher than that of SP according to the Langmuir model analyses. However, the DM model had the highest determinant coefficient (R2) values for both As and Pb adsorption, indicating that the beads had heterogenous adsorption sites with different adsorption affinities. These magnetic beads could be utilized to treat contaminated groundwater.

Effect of Mangrove Biochar Residue Amended Shrimp Pond Sediment on Nitrogen Adsorption and Leaching

Mangrove biochar residue was used for nitrogen adsorption and retention in sediment, which is beneficial for plant germination. The present study investigated the effect of contact time (5–360 min), biochar dosage (0.2–2 g L−1), pH (5–6), and initial concentration (2–10 mg L−1) on NH4+-N and NO3−-N adsorption. Three different adsorption isotherm models were used to fit the experimental data. Column leaching experiments were conducted to investigate the effect of biochar with sediment from a shrimp pond on nitrogen leaching at varying biochar dosages (0–8% w/w). The results showed that the maximum percentage of both NH4+-N and NO3−-N adsorption was achieved at an equilibrium contact time of 240 min, with an adsorbent dosage of 2 g L−1, and pH at 5.5 and 5, respectively. The adsorption of NH4+-N and NO3−-N were fitted to the Freundlich model and the adsorption process followed the physisorption and ion exchange. The addition of 8% biochar reduced both cumulative water volume and nitrogen leaching from the sediment. The biochar amendment increased the relative abundance of nitrifying and denitrifying bacteria in the sediment. This result suggested that biochar amended with sediment could be useful for nitrogen loss reduction.

Adsorptive removal of Pb(II) and Cd(II) ions from aqueous solution onto modified Hiswa iron-kaolin clay: Equilibrium and thermodynamic aspects

In view of promising adsorption efficiency of clay based materials, a modified iron-kaolin clay was used as an adsorbent of Pb(II) and Cd(II) ions from aqueous solutions. The effects of various experimental parameters, such as initial metal ions concentration, contact time, temperature and pH were investigated. The Langmuir and Freundlich adsorption isotherm models were applied to the experimental equilibrium data at different temperatures. The maximum adsorption capacities of Pb(II) and Cd(II) ions were 76.92 and 75.19 (mg/g), respectively. Thermodynamic parameters such as the change of Gibbs free energy, enthalpy and entropy of adsorption were also calculated and it was found that the lead and cadmium ions uptake by modified kaolin clay is endothermic and spontaneous in nature.

Adsorption Isotherm of Carbon Microparticles Prepared from Pumpkin (Cucurbita maxima) Seeds for Dye Removal

This study aims to evaluate the adsorption isotherm of carbon microparticles prepared from pumpkin (Cucurbita maxima) seeds for adsorbing curcumin (as a model of dye). The results were derived and compared using the kinetics approach based on several standard adsorption isotherm models, namely the Langmuir, Temkin, Freundlich, and Dubinin-Radushkevich models. The second aim is to evaluate the effects of carbon particle size (from 100 to 1000 mm) on the adsorption characteristics. The experimental results showed that the adsorption on the surface of carbon microparticles occurred in monolayer with a physical phenomenon. This is because the active areas are located only on the outer surface of carbon and no surface structure in the carbon is available. This is confirmed by the fact that the produced carbon has less porosity and the pores themselves are mostly produced from the release of inorganic contents during carbon synthesis, while the amount of inorganic content is very less. The confirmation of the adsorption profile was also achieved by testing various sizes of carbon microparticles. Smaller particles have direct impacts on the improvement of adsorption capacity, which is due to the existence of a larger surface area, a larger number of adsorption sites, and additional cooperative adsorption, i.e. adsorbate-adsorbate interaction. Understanding the adsorption phenomena occurring on carbon particles is useful for further developments and applications, such as those of catalysts and adsorbents, especially concerning the production of carbon materials from organic waste.

Adsorption Characteristics of Phosphate Ions by Pristine, CaCl2 and FeCl3-Activated Biochars Originated from Tangerine Peels

This study has evaluated the removal efficiencies of phosphate ions (PO43−) using pristine (TB) and chemical-activated tangerine peel biochars. The adsorption kinetics and isotherm presented that the enhanced physicochemical properties of TB surface through the chemical activation with CaCl2 (CTB) and FeCl3 (FTB) were helpful in the adsorption capacities of PO43− (equilibrium adsorption capacity: FTB (1.655 mg g−1) > CTB (0.354 mg g−1) > TB (0.104 mg g−1)). The adsorption kinetics results revealed that PO43− removal by TB, CTB, and FTB was well fitted with the pseudo-second-order model (R2 = 0.999) than the pseudo-first-order model (R2 ≥ 0.929). The adsorption isotherm models showed that the Freundlich equation was suitable for PO43− removal by TB (R2 = 0.975) and CTB (R2 = 0.955). In contrast, the Langmuir equation was proper for PO43− removal by FTB (R2 = 0.987). The PO43− removal efficiency of CTB and FTB decreased with the ionic strength increased due to the compression of the electrical double layer on the CTB and FTB surfaces. Besides, the PO43− adsorptions by TB, CTB, and FTB were spontaneous endothermic reactions. These findings demonstrated FTB was the most promising method for removing PO43− in waters.