Assessment of the calcium-silicate Polonite as a sorbent for thin-layer capping of metal contaminated sediment.

Sediments contaminated with hazardous metals pose risks to humans and wildlife, yet viable management options are scarce. In a series of laboratory experiments, we characterized Polonite® - an activated calcium-silicate - as a novel sorbent for thin-layer capping of metal-contaminated sediments. We tested a fine-grained by-product from the Polonite production as a cheap and sustainable sorbent. First, Polonite was reacted with solutions of Cu, Pb, and Zn, and the surface chemistry of the Polonite was examined using, e.g., scanning electron microscopy to investigate metal sorption mechanisms. Batch experiments were conducted by adding Polonite to industrially contaminated harbor sediment to determine sorption kinetics and isotherms. Importantly, we measured if the Polonite could reduce metal bioavailability to sediment fauna by performing digestive fluid extraction (DFE). Finally, a cap placement technique was studied by applying a Polonite slurry in sedimentation columns. The results showed rapid metal sorption to Polonite via several mechanisms, including hydroxide and carbonate precipitation, and complexation with metal oxides on the Polonite surface. Isotherm data revealed that the sediment uptake capacity (Kf) for Cu, Pb, and Zn increased by a factor of 25, 21, and 14, respectively, after addition of 5% Polonite. The bioavailability of Cu, Pb, and Zn was reduced by 70%, 65%, and 54%, respectively, after a 25% Polonite addition. In conclusion, we propose that sediment treatment with low doses of the Polonite by-product can be a cheap, sustainable, and effective remediation method compared to other more intrusive methods such as dredging or conventional isolation capping.

Efficient loading of nano Mn particles on calcined laterite soil (Lt-nMn) for higher removal of As(III) ions from groundwater: adsorption and eco-scale analysis.

Occurrence of arsenic in the groundwater has become a cause for concern in many countries. The presence of As(III) species in the groundwater had been one of the biggest challenges for the water workers especially in the southeast Asian countries. Nano based adsorption techniques are gaining attention among researchers for the removal of arsenic ions. However, synthesis of nano-adsorbents is a costly affair. Therefore, the present study utilized the cheap and readily available laterite soil as a base material for nano coating. Nano sized manganese (nMn) particles were synthesized by chemical reduction method and later coated on calcined laterite (Lt-nMn). Coating with 0.1 M nMn provided the best As(III) removal efficiency. The prepared material was characterised for its morphological and surface properties. Phase analysis using XRD (X-ray diffraction) showed the presence of zero valent manganese species, which assisted in adsorption. Adsorption studies were conceded by selecting the different affecting parameters such as contact time, concentration, dose, temperature, and pH. Very high removal in less time regime led to the investigation of the oxidation mechanism. Phosphate and sulphate anions insignificantly reduced the removal efficiency. Langmuir model for the sorption isotherms and pseudo-second order kinetic model for the sorption kinetics symbolized the experimental data. Sustainability studies in terms of eco-scaling and cost analysis were performed for the applied method of production of the nano materials. Adsorber design analysis was also conducted to estimate the required amount of Lt-nMn particles for achieving the desired equilibrium As(III) concentration.

Use of adsorption-influencing parameters for designing the batch adsorber and neural network-based prediction modelling for the aqueous arsenate removal using combustion synthesised nano-alumina.

Removal of arsenic from water is of utmost priorities on a global scenario due to its ill effects. Therefore, in the present study, aluminium oxide nano-particles (nano-alumina) were synthesised via solution combustion method, which is self-propagating and eco-friendly in nature. Synthesised nano-alumina was further employed for arsenate removal from water. Usually, pre-oxidation of arsenite is performed for better removal of arsenic in its pentavalent form. Thus, arsenate removal as a function of influencing parameters such as initial concentration, dose, pH, temperature, and competing anions was the prime objective of the present study. The speciation analysis showed that H2AsO4- and HAsO42- were co-existing anions between pH 6 and 8, as a result of which higher removal was observed. Freundlich isotherm model was well suited for data on adsorption. At optimal temperature of 298 K, maximum monolayer adsorption capacity was found as 1401.90 µg/g. The kinetic data showed film diffusion step was the controlling mechanism. In addition, competing anions like nitrate, bicarbonate, and chloride had no major effect on arsenate removal efficiency, while phosphate and sulphate significantly reduced the removal efficiency. The negative values of thermodynamic parameters ΔH° (- 23.15 kJ/mol) established the exothermic nature of adsorption, whereas the negative values of ΔG° (- 7.05, - 6.51, - 5.97, and - 5.43 kJ/mol at 298, 308, 318, and 328 K respectively) indicated the spontaneous nature of the process. The best-fitted isotherm was used to design a batch adsorber to estimate the required amount of aluminium oxide nano-particles for achieving the desired equilibrium arsenate concentration. Nano-alumina was also applied to treat the collected arsenic-contaminated groundwater from actual field. Experimental data were used to develop a neural network-based model for the effective prediction of removal efficiency without carrying out any extra experimentation.

As(V) removal using biochar produced from an agricultural waste and prediction of removal efficiency using multiple regression analysis.

Arsenic contamination in drinking water is a matter of concern for many countries. An efficient and low-cost solution for this hazard is essentially needed on urgent basis. Therefore, in this study, banana pith (an agricultural waste) was used for biochar production and later it was modified with iron and applied for arsenic adsorption from aqueous solution. Produced biochar was characterized for proximate, ultimate, and surface analyses. Interestingly, after iron impregnation, the surface area of biochar increased (31.59 m2/g) by nearly 8 times. Morphological analysis showed that iron particles firmly held within the pores after impregnation. Arsenate (As(V)) adsorption behavior of iron-impregnated banana pith biochar was evaluated through a batch study by considering various parameters like dose, concentration, pH, temperature, and competing anions. Compared to impregnated biochar, raw biomass and its biochar showed a lesser affinity for arsenate in aqueous solution. The adsorption isotherm of As(V) on banana pith biochar was covered in the temperature range of 298 to 318 K, and kinetic data of adsorption was experimentally generated at 298 K. Langmuir model for the sorption isotherms and pseudo-second-order kinetic model for the sorption kinetics represented the experimental data. The thermodynamic study showed negative Gibb's free energy (- 46.88 kJ/mol at 298 K, - 48.58 kJ/mol at 308 K, - 50.73 kJ/mol at 318 K) that suggested spontaneity of the adsorption process. Negative enthalpy (ΔH° = - 10.55 kJ/mol) showed exothermic nature of adsorption of arsenic, while negative entropy (ΔS° = 0.123 kJ/mol.K) suggested enthalpy-driven adsorption process. Mechanism of arsenic adsorption onto iron-impregnated banana pith biochar has also been discussed in detail. Based on the experimental observation, a predictive model for arsenate removal has been developed in this study. The findings of the present study elucidated that iron-impregnated banana pith biochar can be used as a low-cost adsorbing material for As(V) from aqueous solutions.