Removal of arsenic (V) from aqueous solutions using chitosan-red scoria and chitosan-pumice blends

In different regions across the globe, elevated arsenic contents in the groundwater constitute a major health problem. In this work, a biopolymer chitosan has been blended with volcanic rocks (red scoria and pumice) for arsenic (V) removal. The effect of three blending ratios of chitosan and volcanic rocks (1:2, 1:5 and 1:10) on arsenic removal has been studied. The optimal blending ratio was 1:5 (chitosan:volcanic rocks) with maximum adsorption capacity of 0.72 mg/g and 0.71 mg/g for chitosan:red scoria (Ch-Rs) and chitosan:pumice (Ch-Pu), respectively. The experimental adsorption data fitted well a Langmuir isotherm (R-2 > 0.99) and followed pseudo-second-order kinetics. The high stability of the materials and their high arsenic (V) removal efficiency (similar to 93%) in a wide pH range (4 to 10) are useful for real field applications. Moreover, the blends could be regenerated using 0.05 M NaOH and used for several cycles without losing their original arsenic removal efficiency. The results of the study demonstrate that chitosan-volcanic rock blends should be further explored as a potential sustainable solution for removal of arsenic (V) from water

The Use of Bauxite as an Arsenic Filter

AbstractArsenic (As) has the potential to negatively affect soils and groundwater quality, and cause several public health challenges. It is usually concentrated and released during metal mining of ores that contains arsenic-bearing minerals. Remediation strategies are in place to avoid pollution. In this study, bauxite from Awaso, Ghana, was characterised, and its ability to sequester As was tested under varying conditions of temperature, Eh and pH. The study showed that the best particle size in the range utilised was 80% passing 2 mm as it allowed easy percolation, and As removal was about 95%. The reaction is a favourable pseudo-second order reaction that is spontaneous and thermodynamically stable and compares well with the Langmuir Sorption Isotherm. About 80% sorption was achieved within 20 minutes of contact with low desorption rate of less than 1.8%. The study thus concludes that bauxite is a good filter for arsenic. Keywords: Arsenic, Bauxite, Filter, Sorption, Isother

PREPARATION OF RED MUD/GRAPHENE COMPOSITE AND ITS APPLICATION FOR ADSORPTION OF As(III) FROM AQUEOUS SOLUTION

In this study, we produce a red mud/graphene composite (REEG) via electrochemical activation graphite in basic red mud slurry. The adsorption properties for As(III) on REEG were investigated by batch method. The influence of pH (2-12), contact time (0-300 min), and the amount of adsorbent (0.02-0.1 g) on As(III) removal efficiency by the REEG were also determined. Results showed that the equilibrium time, the optimal pH, and mass of adsorbent were 240 min, pH 3.0 and 0.05 g, respectively. The maximum adsorption capacity (qmax) calculated by Langmuir isotherm model was found to be 21.367 mg/g. The results showed that REEG promises to be a good absorbent for As(III) removal from aqueous solution.

Iron Activation of Natural Aluminosilicates to Remove Arsenic from Groundwater

Low-cost adsorbents constituted by Fe-modified-aluminosilicates (laminar and zeolite type minerals) were developed and characterized to be used in the arsenic removal from groundwater. Iron activation was carried out “in situ” by the synthesis and deposition of mesoporous ferrihydrite. Natural iron-rich aluminosilicate was used as reference. All samples were characterized by X-ray diffraction, Raman spectroscopy, BET N2-adsorption, SEM-EDS microscopy and ICP chemical analysis. Experimental results of arsenic sorption showed that iron-poor raw materials were not active, unlike iron activated samples. The iron loading in all activated samples was below 5% (expressed as Fe2O3), whereas the removal capacity of these samples reaches between 200-700 µg of As by g of adsorbent, after reusing between 17 cycles and 70 cycles up to adsorbent saturation. Differences can be associated to mineral structure and to the surface charge modification by iron deposition, affecting the attraction of the As-oxoanion. On the basis of low-cost raw materials, the easy chemical process for activation shows that these materials are potentially attractive for As(V) removal. Likewise, the activation of clay minerals, with natural high content of iron, seems to be a good strategy to enhance the arsenic adsorption ability and consequently the useful life of the adsorbent.Fil: Botto, Irma Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Química Inorgánica; ArgentinaFil: González, María José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Química Inorgánica; Argentina. Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Instituto de Recursos Minerales; ArgentinaFil: Gazzoli, Delia. Universita di Roma La Sapienza. Dipartimento di Chimica; ItaliaFil: Soto, Edgardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Investigación y Desarrollo En Ciencias Aplicadas; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Planta Piloto Multiproposito; Argentin

Development of Green Solvent Modified Zeolite (gsmz) for the Removal of Chemical Contaminants from Water

Sorption represents an important strategy in the remediation of groundwater contamination. As a naturally-occurring mineral with large cation exchange capacity, zeolite is negatively charged and has been widely used as an inexpensive and effective sorbent for the removal of positively charged contaminants. The negative charges of zeolite, however, make it generally ineffective in the sorption of anionic contaminants such as chromate and arsenate. In order to improve the capacity for sorption of anionic species, the surface charge of the zeolite must be modified. Cationic surfactants can be used to alter the surface charge of the minerals so that the negatively charged heavy metals can be removed. The adsorption equilibrium and kinetics data for adsorption of As(V) and Cr(VI) from an aqueous solution onto a green solvent modified zeolite (GSMZ) were determined through batch experiments. A natural zeolite from St. Cloud New Mexico was modified by the surfactant HDmim, from the imidazolium group of chemicals, which are considered as green solvents . The effects of ionic strength and solution pH on the sorption capacity of As(V) and Cr(VI) on GSMZ were evaluated. Our results indicate that pH has little effect on the removal of both As(V) and Cr(VI) on GSMZ. Zeta potential tests show that for the pH range tested (4-9) the surface charge of the modified zeolite is consistently positive. The removal of arsenate and chromate by GSMZ does not appear to be dependent on speciation at different pH. Meanwhile, competition by chloride ions at different ionic strength was found to have an impact on sorption capacity. The Langmuir competition model was applied to experimental adsorption data to determine the extent of competition between the heavy metal ions and chloride anions. Compared to previously modified zeolites, GSMZ performed well, with a sorption maximum for chromate of about 26 mM/kg and a sorption maximum for arsenate of about 12 mM/kg

REMOVAL OF HEAVY METALS FROM WATER USING NATURAL BAUXITE

Bauxite, the principal ore of aluminum is a potential low-cost sorbent to treat heavy metal-contaminated water. This work studied the ability of raw bauxite to adsorb Pb2+, Cu2+ , Ni2+, and Co2+ ions in natural waters and the dependency of the sorption efficiency on the initial metal ion concentration in water, contact time, the ‘type’ of bauxite, and the effect of coexisting metals. Goethite-rich (B1) and kaolinite-rich (B2) bauxites were sampled in Pontotoc County, Mississippi. Single element and multi-element (ME) solutions were prepared by introducing the metals at concentrations of 10, 100, and 500 ppb in lake water. The solutions were left in contact with 0.25 g of prepared bauxite powder over contact periods of 3, 6, 12, 24, and 48 hours without changing other physicochemical parameters. The filtrates were analyzed using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). Bauxite mineralogy was examined using X-ray Diffraction (XRD) and Scanning Electron Microscope with Energy Dispersive X-ray spectroscopy (SEM-EDS). Except in certain Ni2+ -containing systems, bauxite could remove metals from the water. Overall, the percent sorption tends to decrease with increase in initial metal concentration of the metals tested. Some systems particularly Pb2+ - and Cu2+ -containing recorded the highest percent sorption (\u3e90%) at 100 ppb but it dropped (around 20-40%) at 500 ppb. Metal uptake generally increases with increase in initial metal concentration but the increment between the 100 ppb and the 500 ppb systems is often less pronounced. The sorption by B1 is relatively more dependent on the initial metal concentration. Overall, the removal efficiency of B2 is slightly higher. A clear dependency of sorption on contact time was not observed. Bauxite is selective towards Cu2+ and Pb2+ but the near-complete removal of Cu2+ in some systems suggests that Cu2+ is favored. Co2+ and Ni2+ seem to have similar affinities toward bauxite, but Ni2+ showed negative percent sorption values at certain longer contact times and higher concentrations. The removal efficiencies of both bauxites decreased in the ME-experiments. Adsorption is possibly Langmuirtype, suggesting chemisorptive monolayer formation. Fe-Al Oxyhydroxide and clay surfaces are the possible adsorption sites in bauxite that bind metals via specific adsorption and ion exchange