Biosorption of toxic metal ions (Cr+6, Cd2+) and nutrients (PO43-) from aqueous solution by diatom biomass

This paper evaluates diatom biomass as a biosorbent for removing Cr⁺⁶, Cd²⁺, and PO₄^3- ions from water. The diatom was characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), and Scanning Electron Microscopy (SEM-EDS) for its crystallinity, functional groups, and morphology. A batch sorption study was conducted to evaluate the parameters influencing Cr⁺⁶, Cd²⁺, and PO₄^3- ions adsorption, and the mechanisms were explored. The FTIR spectra revealed Si-O, O-H, N-H, and C-O as the main functional groups present on the surface of the adsorbent. The SEM showed a rough and irregular-shaped morphology, while the EDS indicated that the diatom biomass is an aluminosilicate material. The rate-limiting steps for Cr⁺⁶ and Cd²⁺ were pseudo-first order, and pseudo-second order sorption favored PO₄^3- based on their R² values. Moreover, the dominant adsorption model that best described the equilibrium data was the Freundlich isotherm. The maximum adsorption capacities obtained for Cr⁺⁶ was 5.66 (mg/g), and Cd²⁺ was 5.27 (mg/g) at 313 K while PO₄^3- was 19.13 (mg/g) at 298 K. The thermodynamic data revealed that the reaction was endothermic for Cd²⁺ and exothermic for Cr⁺⁶ and PO₄^3-, respectively. Diatom biomass was observed to be a promising bio-sorbent for removing Cr⁶⁺, Cd²⁺ and PO₄^2- from wastewater.

Synthesis of porous hydroxysodalite from aluminosilicate rich clay soils: application towards fluoride and pathogen removal

This article discussed the potential application of hydrothermally synthesized porous hydroxysodalite material synthesized from aluminosilicate clay material as a multifunctional adsorbent for fluoride and pathogen removal from groundwater. The efficiency of the material towards fluoride removal was evaluated using batch experiments while the efficacy against the E. coli strain was evaluated using well-assay diffusion method. The material showed a maximum fluoride adsorption capacity of 6.01 mg/g at initial concentration range of 5 to 100 mg/L when 1 g/100 mL adsorbent dosage was used at initial pH of 6 ± 0.5 after agitation time of 10 min. The adsorption kinetics data fitted better to pseudo first order of reaction kinetics indicating the dominance of physiosorption adsorption mechanism while the adsorption isotherm data showed better fit to both Langmuir and Freundlich adsorption isotherm model confirming monolayer and multilayer adsorption. The material was successfully regenerated and reused for up to eight successive regeneration-reuse cycles. However, its efficiency was inhibited by the presence of Cl^- and CO₃^2-. The material also proven to have antimicrobial activity against E. coli strain. This study concluded that the porous hydroxysodalite material prepared in this study can be used as a multifunctional adsorbent for fluoride and pathogen removal from groundwater.

Effect of Microwave-Assisted Aqueous Two-Phase Extraction of α-Solanine from S. retroflexum and Analysis on UHPLC-qTOF-MS

A new, fast and efficient method, hyphenated microwave-assisted aqueous two-phase extraction (MA-ATPE) was applied in the extraction of α-solanine from Solanum retroflexum. This environmentally friendly extraction method applied water and ethanol as extraction solvents. Central composite design (CCD) was performed which included numerical parameters such as time, mass of plant powder and microwave power. The categorical factors included the chaotrope — NaCl or the kosmotrope — Na2CO3. Fitting the central composite design response surface model to the data generated a quadratic model with a good fit (R2 = 0.920). The statistically significant (p < 0.05) parameters such as time and mass of plant powder were influential in the extraction of α-solanine. Quantification of α-solanine was achieved using a robust and sensitive feature of the ultra-high performance quadrupole time of flight mass spectrometer (UHPLC-qTOF-MS), multiple reaction monitoring (MRM). The optimized condition for the extraction of α-solanine in the presence of NaCl and Na2CO3 was a period of 1 min at a mass of 1.2 g using a microwave power of 40%. Maximal extraction of α-solanine was 93.50 mg kg−1 and 72.16 mg kg−1 for Na2CO3 and NaCl, respectively. The synergistic effect of salting-out and microwave extraction was influential in extraction of α-solanine. Furthermore, the higher negative charge density of the kosmotrope (Na2CO3) was responsible for its greater extraction of α-solanine than chaotrope (NaCl). The shorter optimal extraction times of MA-ATPE make it a potential technique that could meet market demand as it is a quick, green and efficient method for removal of toxic metabolites in nutraceuticals.

Advances in the development of biopolymeric adsorbents for the extraction of metabolites from nutraceuticals with emphasis on Solanaceae and subsequent pharmacological applications

Biopolymers are renowned for their sustainable, biodegradable, biocompatible and most of them have antitoxic characteristics. These versatile naturally derived compounds include proteins, polynucleotides (RNA and DNA) and polysaccharides. Cellulose and chitosan are the most abundant polysaccharides. Proteins and polysaccharides have been applied as emulsifiers. Additional applications of proteins and polysaccharides include cosmetics, food and wastewater treatment for adsorption of dyes and pesticides. However, more interesting applications of biopolymers are emerging, such as use in transport systems for delivery of plant derived nutraceuticals to sites of inflammation, due to its inherent ability to immobilize different biological and chemical systems. This review aims to give a summary on new trends and complement what is already known in the development of polysaccharides and proteins as adsorbents of nutraceutical compounds. The application of polysaccharides/protein containing the adsorbed Solanum derived nutraceutical compounds for drug deliveryis also reviewed.

Synthesis and evaluation of the oil removal potential of 3-bromo-benzimidazolone polymer grafted silica gel

This work reports the synthesis of 3-bromo-benzimidazolone using melt condensation, its polymerization and functionalization on silica which was extracted from diatomaceous earth in our previous work. The synthesized compounds were characterized using FTIR, NMR, SEM-EDS and TEM. The FTIR and NMR spectra of the synthesized benzimidazolones showed the compounds to have several functional groups: A band due to Si-O-C at 1085.41 cm-1, a broad band at 3380 cm-1 and chemical shifts: positive distortionless enhancement by polarization transfer (DEPT) 13C peaks (indicating lack of CH2 and CH3 groups), 1H NMR - 11.053 ppm (N-H), 7.086 ppm (Ar-H); 13C NMR - 155.34 ppm (C[double bond, length as m-dash]O), 101.04 ppm (C-Br) characteristic of benzimidazolones. SEM-EDS of the functionalized silica showed a rough irregular morphology with Si and O as the major elements. Carbon was also present indicating that silica was successfully functionalized with 3-bromo-benzimidazolone and TEM showed interconnected smear-like particles arranged irregularly. The functionalized silica was then applied in the treatment of oily wastewater and factors like initial oil concentration, adsorption dosage and time were optimized using the central composite design of response surface methodology in the design expert software. The amount of oil adsorbed was obtained by quantifying the total organic carbon using TOC test kits. Results showed that the optimum conditions for oil removal were 6650 mg L-1 oil concentration, with adsorbent dosage of 0.004 g and a contact time of 16 h. Under these conditions, the percentage adsorption was 97.9% with a desirability of 0.99. The materials were therefore seen to be applicable to field wastewaters.

Response Surface Optimization of Oil Removal Using Synthesized Polypyrrole-Silica Polymer Composite

The severity of oil pollution, brought about by improper management, increases daily with an increase in the exploration and usage of oil, especially with an increase in industrialization. Conventional oil treatment methods are either expensive or time consuming, hence the need for new technologies. The aim of this research is to synthesize polypyrrole-modified silica for the treatment of oily wastewater. Pyrrole was copolymerized with silica in the presence of ferric chloride hexahydrate by adding 23 mL of 117.4 g/dm³ ferric chloride hexahydrate drop wise to a silica-pyrrole mixture (1:2.3). The mixture was stirred for 24 h, filtered and dried at 60 °C for 24 h. The composite was then characterized using FTIR and SEM/EDX. A central composite model was developed in design expert software to describe the efficiency of oil removal using the polypyrrole-modified silica under the influence of initial oil concentration, adsorbent dosage and contact time. The synthesized adsorbent had FTIR bands at 3000–3500 cm⁻¹ (due to the N-H), 1034 cm⁻¹ (attributed to the Si-O of silica), 1607 cm⁻¹ and 1615 cm⁻¹ (due to the stretching vibration of C=C of pyrrole ring). The adsorption capacity values predicted by the central composite model were in good agreement with the actual experimental values, indicating that the model can be used to optimize the removal of oil from oily wastewater in the presence of polypyrrole-modified silica. The adsorbent showed excellent oil uptake when compared with similar materials. The optimum conditions for oil removal were 7091 mg/L oil concentration, 0.004 g adsorbent dosage and contact time of 16 h. Under these conditions, the percentage of oil adsorption was 99.3% and adsorption capacity was 8451 mg/g. As a result of the low optimum dosage and the lack of agitation, the material was found to be applicable in the remediation of field wastewater.

Geochemical fractionation of hazardous elements in fresh and drilled weathered South African coal fly ashes

The chemical reactions of dry-disposed ash dump, ingressed oxygen, carbon dioxide, and infiltrating rainwater affect mineralogical transformation, redistribution, and migration of chemical species. Composite samples of weathered coal fly ash taken at various depths and fresh coal fly ash were examined using organic petrographic, X-ray diffraction, X-ray fluorescence techniques, and successive extraction procedures. Results obtained show relative enrichment of glass, Al-Fe-oxides, calcite, and tridymite in the weathered CFA, but the fresh CFA is enriched in mullite, inertinite, maghemite, and ettringite. The enrichment of the weathered CFA in amorphous glass suggests higher reactivity when compared to fresh CFA. The evident depletion of soluble oxides in the weathered CFA is attributed to flushing of the soluble salts by percolating rainwater. Comparative enrichment of examined elements in water-soluble, exchangeable, reducible, and residual fractions of the weathered CFA is partly due to the slow release of adsorbed chemical species from the alumina-silicate matrix and diffusion from the deeper sections of the particles of coal fly ash. Sodium and potassium show enrichment in the oxidisable fraction of fresh CFA. The estimated mobility factor indicates mobility for Ca, Mg, Na, Se, Mo, and Sb and K, Sr, V, Cu, Cr, Se, and B in fresh and weathered CFAs, respectively.

Natural weathering in dry disposed ash dump: Insight from chemical, mineralogical and geochemical analysis of fresh and unsaturated drilled cores

Some existing alternative applications of coal fly ash such as cement manufacturing; road construction; landfill; and concrete and waste stabilisation use fresh ash directly collected from coal-fired power generating stations. Thus, if the rate of usage continues, the demand for fresh ash for various applications will exceed supply and use of weathered dry disposed ash will become necessary alternative. As a result it's imperative to understand the chemistry and pH behaviour of some metals inherent in dry disposed fly ash. The bulk chemical composition as determined by XRF analysis showed that SiO2, Al2O3 and Fe2O3 were the major oxides in fresh ash and unsaturated weathered ashes. The unsaturated weathered ashes are relatively depleted in CaO, Fe2O3, TiO2, SiO2, Na2O and P2O5 due to dissolution and hydrolysis caused by chemical interaction with ingressing CO2 from the atmosphere and infiltrating rain water. Observed accumulations of Fe2O3, TiO2, CaO, K2O, Na2O and SO3 and Zn, Zr, Sr, Pb, Ni, Cr and Co in the lower layers indicate progressive downward movement through the ash dump though at a slow rate. The bulk mineralogy of unsaturated weathered dry disposed ash, as determined by XRD analysis, revealed quartz and mullite as the major crystalline phases; while anorthite, hematite, enstatite, lime, calcite, and mica were present as minor mineral phases. Pore water chemistry revealed a low concentration of readily soluble metals in unsaturated weathered ashes in comparison with fresh ash, which shows high leachability. This suggests that over time the precipitation of transient minor secondary mineral phases; such as calcite and mica might retard residual metal release from unsaturated weathered ash. Chloride and sulphate species of the water soluble extracts of weathered ash are at equilibrium with Na+ and K+; these demonstrate progressive leaching over time and become supersaturated at the base of unsaturated weathered ash. This suggests that the ash dump does not encapsulate the salt or act as a sustainable salt sink due to over time reduction in pore water pH. The leaching behaviours of Ca, Mg, Na+, K+, Se, Cr and Sr are controlled by the pH of the leachant in both fresh and unsaturated weathered ash. Other trace metals like As, Mo and Pb showed amphoteric behaviour with respect to the pH of the leachant. The precipitation of minor quantities of secondary mineral phases in the unsaturated weathered ash has significant effects on the acid susceptibility and leaching patterns of chemical species in comparison with fresh ash. The unsaturated weathered ash had lower buffering capacity at neutral pH (7.94-8.00) compared to fresh (unweathered) ash. This may be due to the initial high leaching/flushing of soluble basic buffering constituents from fly ash after disposal. The overall results of the acid susceptibility tests suggest that both fresh ash and unsaturated weathered ash would release a large percentage of their chemical species when in contact with slightly acidified rain. Proper management of ash dumps is therefore essential to safeguard the environmental risks of water percolation in different fly ashes behaviour.