Assessment of heavy metal pollution from anthropogenic activities and remediation strategies: A review.

Biochar modification to enhance sorption of inorganics from water

Recently, biochar has received significant attention, especially for the removal of potentially toxic elements (PTEs) from water and wastewater. No review has been focused on the potential use of wood-based biochar (WB) for the removal of PTEs in water and wastewater. Here, we have critically reviewed the (i) preparation and characterisation of WB; (ii) removal efficiency of WB for PTEs in water with respect to its physicochemical characteristics, biochar/water ratio, pH, and sorption system; (iii) removal mechanisms of PTEs by WB; (iv) fate of the sorbed PTEs onto WB; and (v) recovery of the sorbed PTEs from the resultant sludge of WB. We also discussed the removal of PTEs by engineered/designer WB as compared to pristine WB. This review demonstrates the overarching scientific opportunities for a comprehensive understanding of using WB as an emerging biosorbent and a promising low-cost and effective material for the remediation of PTEs contaminated water.

Wood-based biochar for the removal of potentially toxic elements in water and wastewater: a critical review

The solid-liquid interface reaction between phosphate rock (PR) and metals (Pb, Cu, and Zn) was studied. Phosphate rock has the highest affinity for Pb, followed by Cu and Zn, with sorption capacities of 138, 114, and 83.2 mmol/kg PR, respectively. In the Pb-Cu-Zn ternary system, competitive metal sorption occurred with sorption capacity reduction of 15.2%, 48.3%, and 75.6% for Pb, Cu, and Zn, respectively compared to the mono-metal systems. A fractional factorial design showed the interfering effect in the order of Pb>Cu>Zn. Desorption of Cu and Zn was sensitive to pH change, increasing with pH decline, whereas Pb desorption was decreased with a strongly acidic TCLP extracting solution (pH = 2.93). The greatest stability of Pb retention by PR can be attributed to the formation of insoluble fluoropyromorphite [Pb(10)(PO(4))(6)F(2)], which was primarily responsible for Pb immobilization (up to 78.3%), with less contribution from the surface adsorption or complexation (21.7%), compared to 74.5% for Cu and 95.7% for Zn. Solution pH reduction during metal retention and flow calorimetry analysis both supported the hypothesis of retention of Pb, Cu, and Zn by surface adsorption or complexation. Flow calorimetry indicated that Pb and Cu adsorption onto PR was exothermic, while Zn sorption was endothermic. Our research demonstrated that PR can effectively remove Pb from solutions, even in the presence of other heavy metals (e.g. Cu, Zn).

https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1014&context=ersc_fac

Understanding the Mechanisms of Lead, Copper, and Zinc Retention by Phosphate Rock

Microporous materials such as zeolites, metal organic frameworks, activated carbons and aluminum phosphates are suitable for catalysis and separation applications. These high surface area materials are invariably produced in particulate forms and need to be transformed into hierarchically porous structures for high performance adsorbents or catalysts. Structuring of porous powders enables an optimized structure with high mass transfer, low pressure drop, good heat management, and high mechanical and chemical stability. The requirements and important properties of hierarchically porous structures are reviewed with a focus on applications in gas separation and catalysis. Versatile powder processing routes to process porous powders into hierarchically porous structures like extrusion, coatings of scaffolds and honeycombs, colloidal processing and direct casting, and sacrificial approaches are presented and discussed. The use and limitations of the use of inorganic binders for increasing the mechanical strength is reviewed, and the most important binder systems, e.g. clays and silica, are described in detail. Recent advances to produce binder-free and complex shaped hierarchically porous monoliths are described and their performance is compared with traditional binder-containing structured adsorbents. Needs related to better thermal management and improved kinetics and volume efficiency are discussed and an outlook on future research is also given.

https://cyberleninka.org/article/n/1017336.pdf

Structuring adsorbents and catalysts by processing of porous powders

The sorption of copper on synthetic hydroxyapatite was investigated using a batch method and radiotracer technique. The hydroxyapatite sample prepared by a wet precipitation process was of high crystallinity with Ca/P ratio of 1.688. The sorption of copper on hydroxyapatite was pH independent ranging from 4 to 6 as a result of buffering properties of hydroxyapatite. The adsorption of copper was rapid and the percentage of Cu sorption was >98% during the first 15–30 min of the contact time. The experimental data for sorption of copper have been interpreted in the term of Langmuir isotherm. The sorption of Cu2+ ions was performed by ion-exchange with Ca2+ cations on the crystal surface of hydroxyapatite under experimental conditions. The competition effect of Zn2+, Fe2+ and Pb2+ towards Cu2+ sorption was stronger than that of Co2+, Ni2+ and Ca2+ ions. The ability of the bivalent cations to depress the sorption of copper on hydroxyapatite was in the following order Pb2+ > Fe2+ > Zn2+ > Co2+ ≈ Ni2+.

Study of sorption processes of copper on synthetic hydroxyapatite

The sorption of nickel on chitosan was studied using batch method. As a tracer was used radioisotope 63 Ni. The effect of pH and contact time to reach sorption equilibrium was investigated. During the sorption of Ni 2? ions occur mostly to ion-exchange reactions on the surface of sorbent. The time to reach the sorption equilibrium of nickel on chitosan was 14 h. The percentage of sorption after 14 h achieved the value of 84 %. On the sorption of nickel used solutions with initial pH in the range from 3.9 to 8.1. In the monitored range of pH after 24 h of contact was the sorption of nickel on chitosan (97 %. The sorption of nickel was reduced by increasing concentrations of Ni 2? ions in the solution. The experimental data for sorption of nickel have been interpreted in the term of Langmuir iso- therm and the value of maximum sorption capacity of nickel on chitosan was 2.71 9 10 -3 mol g -1 .

Sorption of nickel on chitosan

The sorption of nickel on synthetic hydroxyapatite was investigated using a batch method and radiotracer technique. The hydroxyapatite samples used in experiments were a commercial hydroxyapatite and hydroxyapatite of high crystallinity with Ca/P ratio of 1.563 and 1.688, respectively, prepared by a wet precipitation process. The sorption of nickel on hydroxyapatite was pH independent ranging from 4.5 to 6.5 as a result of buffering properties of hydroxyapatite. The adsorption of nickel was rapid and the percentage of Ni sorption on both samples of hydroxyapatite was >98 % during the first 15–30 min of the contact time for initial Ni2+ concentration of 1 × 10−4 mol dm−3. The experimental data for sorption of nickel have been interpreted in the term of Langmuir isotherm and the value of maximum sorption capacity of nickel on a commercial hydroxyapatite and hydroxyapatite prepared by wet precipitation process was calculated to be 0.184 and 0.247 mmol g−1, respectively. The sorption of Ni2+ ions was performed by ion-exchange with Ca2+ cations on the crystal surface of hydroxyapatite under experimental conditions. The competition effect of Co2+ and Fe2+ towards Ni2+ sorption was stronger than that of Ca2+ ions. NH4
 + ions have no apparent effect on nickel sorption.

Adsorption of nickel on synthetic hydroxyapatite from aqueous solutions

The objective of this study was the utilization of three different biochars for pertechnetate removal from aqueous solutions. Biochars were prepared by slow pyrolysis from different feedstocks, characterized by BET, acid–base titration, SEM, XRD and FTIR and tested for their pertechnetate sorption using batch and dynamic techniques. Effect of various physico-chemical parameters such as contact time, pH and the presence of different ions in the solution on the sorption of pertechnetate onto biochars was investigated. Perrhenate as an analogue of pertechnetate was used for modeling of adsorption isotherms.

Sorption and desorption of pertechnetate on biochar under static batch and dynamic conditions

In this work, highly crystalline CdS nanorods (NRs) were successfully synthesized by a facile, one-step solvothermal method. The as-prepared CdS NRs powder was characterized by XRD, FESEM, Raman, PL, XPS, BET, and UV-visible techniques to evaluate the structural, morphological, and optical properties. The photocatalytic performance of the as-synthesized CdS NRs was investigated for the photodegradation of RhB dye under visible light irradiations. It has been found that CdS NRs show maximum RhB degradation efficiency of 88.4% in 120 min. The excellent photodegradation ability of the CdS NRs can be attributed to their rod-like structure together with their large surface area and surface state. The kinetic study indicated that the photodegradation process was best described by the pseudo-first-order kinetic model. The possible mechanism for the photodegradation of RhB dye over CdS NRs was proposed in this paper.

https://www.mdpi.com/2227-9717/9/2/263/pdf

Michal Galamboš

Papers

Study of sorption processes of copper on synthetic hydroxyapatite

Sorption of nickel on chitosan

Adsorption of nickel on synthetic hydroxyapatite from aqueous solutions

Sorption and desorption of pertechnetate on biochar under static batch and dynamic conditions

Visible Light-Driven Photocatalytic Rhodamine B Degradation Using CdS Nanorods