A Brief Review of Recent Results in Arsenic Adsorption Process from Aquatic Environments by Metal-Organic Frameworks: Classification Based on Kinetics, Isotherms and Thermodynamics Behaviors

The Adsorption of Arsenate and Arsenite Ions on Oxidic Substrates Prepared with a Variable-Charge Lithological Material

The adsorption of As(V) and As(III) (0.01-1 mM) on a calcined oxidic lithologic material substrate with pH-dependent surface variable charges, chemically modifiable, was investigated. The substrate was prepared via thermal treatment using a natural lithologic material rich in amphoteric oxides of Fe, Al, Mn and Ti. The calcined substrate was treated with acid media (HCl 0.1) to homogenize the positive charge density on the oxide surface via oxide protonation so that anion adsorption would be favored. A batch experiment was performed on the acid-treated substrate (activated) and non-activated substrate. L-type isotherms were obtained, which fit the Freundlich model. Isotherm constants showed that there was a greater affinity between the activated substrate and As(V) (K = 10.58) compared to As(III) (K = 5.45). The adsorption capacity of the activated substrate was two times greater than that of the non-activated substrate, As(V) (Kact = 10.58 and Knoact = 5.45) vs. As(III) (Kact = 5.45 y Knoact = 2.44), which was due to the greater positive charge density on the activated surface, created by the protonation of the surface oxides. Protons were liberated during the adsorption reaction (As(V): 2.17 × 10-3 and As(III): 0.96 × 10-3 mmol/mL). The forms H2AsO4- and H3AsO3 deprotonated when adsorbed by the surface groups M-OH2+ (M: Fe, Al). Kinetic data showed a second-order process for As(V) adsorption and a first-order process for As(III) adsorption. The adsorption rate on the activated substrate was two times greater compared with the non-activated substrate: As(V) (kact = 3.78 × 10-5 L/mg·min and knoact = 2.16 × 10-5 L/mg·min) vs. As(III) (kact = 0.055 h-1 and knoact = 0.027 h-1). The tested substrate is potentially useful as a low-cost natural material for arsenic removal from contaminated water.

Influence of Phosphate on Arsenic Adsorption Behavior of Si-Fe-Mg Mixed Hydrous Oxide

The arsenic adsorption performance of silicon (Si), iron (Fe), and magnesium (Mg) mixed hydrous oxide containing a Si: Fe: Mg metal composition ratio of 0.05:0.9:0.05 (SFM05905) was investigated. SFM05905 was synthesized by the co-precipitation method. Batch experiments on arsenic adsorption were conducted at various temperatures and concentrations. Adsorption isotherms models were represented by a linearized equations and were insensitive to temperature change. The anion selectivity of SFM05905 at single component was high for arsenite (III), arsenate (V), and phosphate (PO4), indicating that PO4 inhibits arsenic adsorption. The adsorption amount of As (III), As (V), and PO4 were compared using a column packed with granular SFM05905, and an aqueous solution was passed by a combination of several anions that are single, binary, and ternary adsorbate systems. As (III) had the highest adsorption amount; however, As (III) and PO4 were affected by each other under the ternary mixing condition. Although the adsorption amount of As (V) was smaller than that of As (III), it was not affected by other adsorbates in the column experiments. Finally, although the adsorption of both arsenic continued, the adsorbed PO4 gradually desorbed.

Efficiency evaluation of Falcaria vulgaris biomass in Co(II) uptake from aquatic environments: characteristics, kinetics and optimization of operational variables

In the present research, the seeds of Falcaria vulgaris were extracted from the investigated environment and used for crop cultivation. This study has focused on the efficiency evaluation of Falcaria vulgaris biomass (FVB) in cobalt ions removal from aqueous solutions. The biosorbent was characterized using FTIR, BET, EDAX-EDS, and SEM. The optimal conditions were determined by the response surface methodology (RSM) based on a Box-Behnken design (BBD) model. The BBD model had   R 2 ,   R adj 2 and   R pred 2 values of 0.9919, 0.9774, and 0.8929, respectively. The cobalt removal under different conditions of the BBD model varied from 36.14% to 82.11%. Based on the numerical optimization of the quadratic model, the maximum cobalt removal at a biosorbent-to-metal ratio of 10:1, pH = 4.88 and contact time of 70 min was calculated at 80.941%. The high accuracy of the model in predicting the optimal conditions for cobalt adsorption by FVB was confirmed using statistical analysis and validation tests. The adsorption process of FVB also follows a pseudo-second-order kinetic model, which suggests that the rate-controlling step in cobalt removal is the chemical interaction between functional groups in FVB and Co+2 ions. This study shows that FVB, a low-cost biosorbent, can be a suitable candidate for removing heavy metals such as cobalt from aqueous solutions.

The Lantana camara L. stem biomass as an inexpensive and efficient biosorbent for the adsorptive removal of malachite green from aquatic environments: kinetics, equilibrium and thermodynamic studies

Plant biomass is one of the available and economic biomaterials used to remove environmental pollutants. The presence of colored compounds in aqueous solutions is one of the problems that can be solved by biological methods. Herein, the efficiency of available and inexpensive biomass obtained from Lantana camara L. stem for cationic dye uptake has been evaluated. The effect of operational factors, including dosage of L. camara L. stem biomass (LSB), pH of the solution, initial concentration of malachite green (MG), and residence time on the optimal conditions of analyte uptake was studied. The experimental data of adsorption studies fit with P-S-O kinetic (R2=0.999) and L.I.M (R2=0.998), indicating MG dye adsorption onto LSB occurred in monolayers due to its chemical affinity. The maximum uptake capacity of LSB for the removal of MG dye was 100 mg g^-1. Thermodynamic parameters, including ΔG° (from -2.13 to -2.469 kJ  mol-1), ΔH° (+2.916 kJ  mol-1), and ΔS° (+16.934 J  mol-1 K-1) suggested that the adsorption process was endothermic and spontaneous. The results revealed that LSB considerably has potential for adsorptive removal of cationic dyes such as, MG from aquatic environments.