A Comparison Study on the Arsenate Adsorption Behavior of Calcium-Bearing Materials

Removal of Arsenic(V) from wastewater using calcined eggshells as a cost-effective adsorbent

This study investigates calcined eggshells (CES) as an effective adsorbent for the remediation of As(V). Characterization of CES was performed using zeta potential analysis, FTIR, XRD and SEM-EDX. Batch studies were conducted to examine the effects of pH, adsorption kinetics, and adsorption isotherms to assess efficacy. The adsorption of As(V) followed the Langmuir isotherm and pseudo-second-order kinetics, with a maximum capacity of 91.05 mg g⁻1 at pH 6.0 and 298 K. The presence of additional anions such as chloride, sulfate, or nitrate had no significant impact on the biosorption of arsenate. However, the introduction of phosphate ions notably decreased the rate of arsenic adsorption. CES was easily regenerated with an alkaline solution and showed excellent reusability over four cycles. Thermodynamic studies confirmed the spontaneity and feasibility of the biosorption process. This study highlights that CES is a promising adsorbent for As(V) removal from contaminated water.

Adsorption of Heavy Metals Ions from Mining Metallurgical Tailings Leachate Using a Shell-Based Adsorbent: Characterization, Kinetics and Isotherm Studies

This study defines the optimal parameters that allow the use of waste mollusk shells (WS) to remove heavy metals from three mining and metallurgical leachates. First, the influence of parameters such as pH, contact time, initial metal concentration, adsorbent dose and the presence of co-ions in Cu2+, Cd2+, Zn2+ and Ni2+ adsorption was investigated in synthetic solutions. Metal uptake was found to be dependent on the initial pH of the solution, the removal rate increasing with the increase in pH, showing the highest affinity at pH 5–6. The removal efficiency at lower concentrations was greater than at higher values. The competitive adsorption results on bimetallic solutions showed that the adsorption capacity of the sorbent was restricted by the presence of other ions and suppressed the uptake of heavy metals compared to the single adsorption. Cu2+ was the metal that most inhibited the removal of Cd2+, Zn2+ and Ni2+. The Langmuir isotherm provided the best fit to the experimental data for Cu2+, Cd2+ and Zn2+ and the Freundlich isotherm, for Ni2+. The data showed that the maximum adsorption capacity amax for Zn2+, Cd2+ and Cu2+, was 526.32 mg g−1, 555.56 mg g−1 and 769.23 mg g−1, respectively. Sorption kinetics data best fit the pseudo-second-order kinetic model. The results obtained in the tests with three mining and metallurgical leachates showed that WS were effective in simultaneously removing several heavy metals ions such as Cu, Ni, Zn, Cd, Ni, As and Se.

Adsorption performance and its mechanism of aqueous As(III) on polyporous calcined oyster shell-supported Fe-Mn binary oxide

Fe-Mn binary oxide (FMBO) is a promising adsorbent for As(III) removal through combined adsorption and oxidation. The calcined oyster shell-supported Fe-Mn binary oxide (FMBO/OS) adsorbent was synthesized by the co-precipitation method. Results indicated that the calcined oyster shell, as a carrier, improved the stability of FMBO and its adsorption capacity for As(III). The maximum adsorption capacity of FMBO/OS on As(III) reached 140.5 mg·g^-1 . Under pH 5.0 and 25°C, the removal efficiency of FMBO/OS to As(III) solution (C₀  = 10 mg·L^-1 ) reached 87% within 12 h. Moreover, based on the characterization analyses, the removal mechanisms of As(III) were deduced to include the combined adsorption and oxidation process of FMBO and the synergistic effect of oyster shells. This work provides new insights into synthesizing efficient and green adsorbents to remove aqueous As(III). Meanwhile, it provides technical support for reusing waste biomass materials such as the oyster shell. PRACTITIONER POINTS: FMBO/OS was prepared by a simple hydrothermal co-precipitation method. The carrier alleviates the agglomeration of Fe-Mn oxides. The adsorbent shows a strong adsorption capacity of As(III) and good selectivity. The good results benefit from the synergistic effect of calcium arsenate generation. The prepared adsorbent can adsorb arsenic in real samples.