Adsorption behavior of cadmium ions from aqueous solution using pen shells

Stabilization of lead (Pb)- and arsenic (As)-contaminated soil using pen shells (Atrina pectinata)

Pen shells (PS), a type of shellfish, are abundantly consumed, and their inedible shell residues are often discarded near the coast without consideration of reutilization. This study sought to investigate the use of natural pen shells (NPS) and calcined pen shells (CPS) to stabilize Pb and As-contaminated soil. During the investigation, NPS and CPS were applied to the contaminated soil in amounts ranging from 1 to 10 wt% and cured for 28 days. After the curing process, the mineral phase was examined through X-ray powder diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) analysis. The XRD and SEM-EDX results revealed the presence of riversideite and ettringite, which contribute to Pb and As stabilization in the CPS-treated soil. The leachability of Pb and As in the treated soil was further examined with three types of chemical extraction methods. Extraction results using 0.1 M HCl displayed a notable pH fluctuation in the extractant due to the residual amendments (NPS and CPS). The fluctuation resulted in a strong correlation of leached Pb and As with the pH of the extractant, which might hinder an accurate assessment of stabilization. In order to minimize the effect of pH, an EDTA-NH4OAc extraction was employed, suggesting its potential as a suitable assessment method. EDTA-NH4OAc extraction showed a higher effectiveness of CPS than NPS at 10 wt% of input amounts. In the SBET extraction, that uses a strongly acidic solution, a higher As leachability was observed by increasing the addition of CPS, which implied a CPS-related chemical fixation mechanism. The comparison of various extraction methods showed a higher CPS effectiveness as compared to NPS. However, it was recommended that CPS-treated soil required caution in strongly acidic conditions, especially for arsenic. This study explores the applicability of PS, which has not been investigated as an amendment for Pb and As-contaminated soil previously. Furthermore, this study revealed that utilization of various extraction methods is beneficial for gaining a comprehensive understanding of the role of CaCO3-based amendment in Pb and As-contaminated soil.

Scallop shells as biosorbents for water remediation from heavy metals: Contributions and mechanism of shell components in the adsorption of cadmium from aqueous matrix

To ascertain their potential for heavy metal pollution remedy, we studied the adsorption mechanism of cadmium onto scallop shells and the interactions between the heavy metal and the shell matrix. Intact shells were used to investigate the uptake and diffusion of the metal contaminant onto the shell carbonatic layers, as well as to evaluate the distribution of major and trace elements in the matrix. LA-ICPMS measurements demonstrate that Cd is adsorbed on a very thin layer on the inner and outer surfaces of the shell. Structural and thermal analyses showed the presence of 9 wt.-% of a CdCO3 phase indicating that the adsorption is mainly a superficial process which involves different processes, including ion exchange of Ca by Cd. In addition, organic components of the shell could contribute to adsorption as highlighted by different metal uptake observed for shells with different colours. In particular, darker shells appeared to adsorb more contaminant than the white ones. The contribution of the organic shell components on the adsorption of heavy metals was also highlighted by the element bulk content which showed higher concentrations of different metals in the darker specimen. Raman spectroscopy allowed to identify the pigments as carotenoids, confirmed by XRD measurements which highlighted the presence of astaxanthin phases. The results presented here provide new insights into the Cd adsorption mechanism highlighting the important contribution given by the organic components present in the biogenic carbonate matrix. Furthermore, the high efficiency of Cd removal from water by scallop shells, supported by adsorption kinetic and isotherm studies, has been demonstrated.

Use of thermally activated Fenton sludge for Cd removal in zinc smelter wastewater: Mechanism and feasibility of Cd removal

Fenton sludge is a byproduct of the Fenton process that contains large amounts of Fe and Ca. Because of the secondary contamination generated during the disposal of this byproduct, ecofriendly treatment methods are needed. In this study, we used Fenton sludge to remove the Cd discharged from a zinc smelter factory, using thermal activation to enhance the Cd adsorption capacity. Among the various temperatures considered (300-900 °C), the Fenton sludge that was thermally activated at 900 °C (TA-FS-900) adsorbed the highest amount of Cd because of its high specific surface area and high Fe content. Cd was adsorbed onto TA-FS-900 via complexation with C-OH, C-COOH, FeO-, and FeOH and cation exchange with Ca2+. The maximum adsorption of TA-FS-900 was 260.2 mg/g, indicating that TA-FS-900 is an efficient adsorbent, comparable to those reported in the literature. The initial Cd concentration in the zinc smelter wastewater discharged was 105.7 mg/L, 98.4% of which was removed by applying TA-FS-900, suggesting the applicability of TA-FS-900 for real wastewater containing high concentrations of various cations and anions. The leaching of heavy metals from TA-FS-900 was within the EPA standard limits. We concluded that the environmental impact of Fenton sludge disposal can be reduced, and the use of Fenton sludge can add value to the treatment of industrial wastewater in terms of the circular economy and environment.

Effect of humic compost on the adsorption of cadmium (II) in aqueous medium

The humic compost obtained from the treatment of tobacco from smuggled cigarettes (SCT) and industrial sewage sludge (ISS) was evaluated as adsorbent for Cd (II) in aqueous solution, for possible decontamination of water resources. Optimum conditions were found at pH 5 and a 3 g/L adsorbent concentration, which presented 92% Cd (II) removal and maximum adsorption capacity of 28.546 mg/g. The pseudo-second-order kinetic model presented the best fit, pointing 120 min as the time needed to attain a steady state. FTIR and EDX results suggest the formation of coordinated Cd (II) bonds by functional groups between the compost and the solution. The results obtained in real samples showed that, even under different environmental conditions, the Cd (II) adsorption varied between 80.05 and 91.61%. The results indicated that the compost evaluated can be used for remediation of Cd (II)-contaminated water resources.

WITHDRAWN: Heavy metal ions and dyes removal from aqueous solution using Aloevera-based biosorbent: A systematic review

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been withdrawn at the request of the authors, editor and publisher. The publisher regrets that an error occurred which led to the premature publication of this paper. The publisher apologizes to the readers for this unfortunate erro

Key particle properties of shells for cadmium chemisorption

Previous studies on cadmium adsorption of calcium carbonate have found that polymorph, and, crystallinity are influential factors for adsorbing cadmium ions. The predominant factor for cadmium adsorption has yet to be elucidated because these factors are linked. To overcome this, here each factor is investigated separately. First, atmospheric grinding prepared surf clam (aragonite phase) and scallop (calcite phase) shells with similar crystallite sizes and specific surface areas. Using adsorption isotherm models, kinetics, X-ray diffraction analysis, and TEM observations, both calcite and aragonite react with cadmium to form cadmium carbonate. The chemisorption follows the adsorption mechanism reported in the literature. Based on the Langmuir isotherm model fitting, the maximum adsorbed amount for the ground surf clam shells is 633.3 mg/g, while that for scallop shells is 195.8 mg/g. Then fine surf clam shell particles with a similar specific surface area, and with a relatively wide range of the aragonite ratio, and crystallite size are prepared via a combination of grinding and a subsequent calcination process. Our experiments where one explanatory variable is changed at a time demonstrate that the polymorph ratio and crystallite size of the ground shells play key roles in the chemisorption.

Ultrasonic assisted agro waste biomass for rapid removal of Cd(II) ions from aquatic environment: Mechanism and modelling analysis

In this research, dragon fruit peel, an agro-waste was used to prepare the new adsorbent for the removal of Cd(II) ions from the aquatic environment. The characterization techniques of SEM, FTIR and EDX for the prepared materials have been studied. The influential parameters for Cd(II) ions were experimented and identified the probable conditions for the maximum adsorption of Cd(II) ions. The investigations on isotherms, kinetics, and thermodynamics for Cd(II) ions removal were examined. Adsorption isotherm data was well discussed with Langmuir model based on the obtained good correlation coefficient and error values. Moreover, it follows the pseudo-first-order and exothermic process. The values of monolayer adsorption capacity of surface-modified dragon fruit peel (SMDFP) and ultrasonic-assisted dragon fruit peel (UADFP) was determined to be 7.469 and 24.76 mg/g at an equilibrium condition, respectively. This study exposed that ultrasonic-assisted dragon fruit peel can be a suitable adsorbent for Cd(II) ions removal from the water environment.

Removal of Cd(II) using dithiocarboxyl cornstalk and the waste filtrate

A novel adsorbent, called dithiocarboxyl cornstalk (DTCS), was developed, and the effects of various parameters on the adsorption performance for Cd(II) with DTCS were investigated in this work. The results suggested that DTCS presented the efficient removal capacity for Cd(II) when the pH values, adsorption temperature, and oscillation rate were 3.0 to 6.0, 313 K, and 150 rpm, respectively. The adsorption kinetic data were more agreed with pseudo-second-order kinetic model, and the isotherm data could be characterized by Freundlich model. The thermodynamic data indicated the adsorption process was endothermic and spontaneous. The FTIR and SEM confirmed the chemisorption between Cd(II) and DTCS. Furthermore, to eliminate the secondary pollution, the waste filtrate generated in the preparation of DTCS was employed to remove Cd(II) through flocculation experiments. The results showed that the waste filtrate is a potential flocculant for the treatment of wastewater containing Cd(II).

Sequential removal and recovery of cadmium ions (Cd2+) using photocatalysis and reduction crystallization from the aqueous phase

The removal of cadmium ions using photocatalysis, reduction crystallization and their sequencial system.

Adsorption of cadmium, nickel and lead ions: equilibrium, kinetic and selectivity studies on modified clinoptilolites from the USA and RSA

The performance of modified clinoptilolites (zeolites) from two different sources (South Africa and the USA) for the adsorption of Ni²⁺, Cd²⁺ and Pb²⁺ from synthetic industrial effluent contaminated with metal concentration levels at 50, 150 and 500 ppm was evaluated. The selectivity of the clinoptilolite for the adsorption of Ni²⁺, Cd²⁺ and Pb²⁺ was investigated with mixed feed solutions containing all three ions in equal concentrations and single-component concentrations containing only one of the ions. The homoionic forms of the clinoptilolite were made of Na⁺, K⁺ and Ca²⁺. Batch experiments were then conducted to measure the uptake of metals by the zeolites. The zeolites were characterised using SEM, XRD and BET. The South African clinoptilolite showed a higher surface area and pore volume (17.52m²/g and 0.047cm³/g respectively) than the USA zeolite (12.26m²/g and 0.028cm³/g respectively) for the Na⁺ homoionic form. According to the equilibrium studies, the selectivity sequence was found to be Pb²⁺ > Cd²⁺ > Ni²⁺, with good fits being obtained using Langmuir and Freundlich adsorption isotherms for low metal concentrations. Examples of equilibrium adsorption capacities for RSA and USA clinoptilolite modified with Na⁺ for Pb were 26.94 mg/g and 27.06 mg/g when RSA-Na⁺ and USA-Na⁺ were used respectively. The adsorption was found to depend on the homoionic form of the zeolite and to a lesser extent the source of the zeolite. The selectivity of a particular zeolite for a particular heavy metal can be altered by the homoionic form of the zeolite. Overall, the adsorption capacity of the USA clinoptilolite was higher than the adsorption capacity of the SA clinoptilolite, revealing the potential of clinoptilolite in metal-polluted industrial effluent treatment.