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Oloo CM, Onyari JM, Wanyonyi WC, Wabomba JN, Muinde VM. "Adsorptive removal of hazardous crystal violet dye form aqueous solution using Rhizophora mucronata stem-barks: Equilibrium and kinetics studies." Environmental Chemistry and Ecotoxicology. In Press. AbstractEnvironmental Chemistry and Ecotoxicology

Description
Adsorption of crystal violet (CV) dye from aqueous solution using dried bark powder of mangrove species Rhizophora mucronata was studied. Characterization of adsorbent was done using FTIR and SEM. Batch experiment was carried out to examine the viability of using mangrove bark for adsorption of CV dye from aqueous solutions under different process conditions. The result revealed that removal of CV increased with contact time, adsorbent dose, initial dye concentration and decreased with increased particle size and ionic strength. pH 7 was the optimum pH for CV dye removal. The adsorption equilibrium for CV dye by Rhizophora mucronata stem-bark was attained within 60 min with removal efficacy of up to 99.8%. Pseudo-second-order kinetic model was best used to describe sorption kinetics while Freundlich isotherm model was appropriate for describing adsorption isotherm. The results demonstrated …

2018
Wambu EW, Attahiru S, Shiundu PM, wabomba J. "Removal of heavy-metals from wastewater using a hydrous alumino-silicate mineral from Kenya." Bulletin of the Chemical Society of Ethiopia. 2018;32(1):39-51. AbstractBulletin of the Chemical Society of Ethiopia

Description
Heavy metals’ discharge into the environment continues to pose grave concerns around the world. The efficacy of a hydrous alumino-silicate clay (AlSiM) coming obtained from some regions of Kenya to sorb heavy-metal ions from water has been evaluated in batch tests taking into account changes in adsorbent dose, pH, contact time, and temperature. Complete metal removals, from water containing up to 66 mg/L of Pb (II) was achieved using this material at pH value of 5 over a temperature range of 289–333 K. The adsorption data fitted both the Langmuir and the Dubinin-Radushkevich isotherms with R 2> 0.99. The DR adsorption energy (− 11.7 kJ/mol) indicated that chemisorption was the primary reaction in the adsorption process and the derived∆ G 0 value (− 7.45 kJ/mol) was consistent with the spontaneity of the adsorption process. The kinetic analyses indicated a film-diffusion and surface-chemisorption controlled process. Verification of the initial results on heavy metals-containing wastewaters obtained from a tannery and a leather processing industries revealed excellent adsorption efficacies of AlSiM for Cr 3+(99− 100%), Fe 3+(96− 98%), Mn 2+(85− 97%) and Zn 2+(78− 86%). The use of AlSiM as a plausible low-cost adsorbent for heavy-metal decontamination of industrial effluents has therefore been demonstrated.

2017
Muinde V, Onyari JM, Wamalwa BM, Wabomba J. "Adsorption of Malachite Green from Aqueous Solutions onto Rice Husks: Kinetic and Equilibrium Studies." Journal of Environmental Protection. 2017;8(03):215-230 . AbstractJournal of Environmental Protection

A study was done to evaluate the removal of a cationic dye from simulated waste water onto rice husks (RH). Spectroscopic methods such as FTIR and SEM/EDX were used for adsorbent characterization. Experimental dependency on solution pH, initial dye concentration, agitation speed, adsorbentparticle size, temperature of the solution and contact time was evaluated. The adsorption data was tested using both Langmuir and Freundlich isotherms. The data fitted well into Langmuir isotherm model with a monolayer adsorption capacity of 6.5 mg/g. Further, the separation factor (RL) value was less than unity indicating a favorable adsorption process. Adsorption kinetics was determined using pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The results showed that the adsorption of malachite green onto rice husks followed pseudo-second-order model with a determination coefficient of 0.986. This work has revealed that rice husks have a great potential to sequester cationic dyes from aqueous solutions and therefore it can be utilized to clean contaminated effluents.

2011
Wabomba JN. Kinetics and equilibrium studies of single and multi-component metal ion sorption on a micaceous mineral of kenyan origin.. Nairobi: University of Nairobi; 2011. Abstract

Water pollution by Chemicals is of great public concern. Improvements in the quality and availability of water are often possible at relatively low costs. The objective of this work was to test the efficacy and applicability of a Micaceous mineral of Kenyan origin (herein referred to as Mica-K or the mineral) in the removal of toxic divalent heavy metal ions from water and wastewater systems. Mica-K was characterized and utilized in study of single and multi-component removal of Cu2+, Cd2+ and Zn2+ ions from aqueous solution over wide range of initial metal ion concentrations (25 mglL to 500 mg/L), contact duration (0-3hrs), sorbent dose (0.5-10 gl25ml or 20-400glL), pH (1.5 to 7.5), and temperature (293 to 333 K). The sorption pattern of Cu2+, Cd2+ and Zn2+ ions onto the micaceous mineral followed Langmuir, Freundlich, and DubininKaganer-Radushkevich isotherms. The dependence of heavy metal adsorption on pH was different for each metal ion. The removal of Zn2+ was about 0% at pH 2 and it increased to 93% at pH 7.4. For Cu2+, 72% was removed at pH 2.5 and it increased to 98% at pH 7.4. Cd2+, removal increased with increasing pH from 45% at pH 1.5 to 93% at pH 7.4. In all cases, over 93% of all the three metals were removed at pH 7.4. Metal ion removal was however, considerably affected by the presence of competing metal ions in solution. • 0 0 0 2-"- 2+ 2+. . Thermodynarmc parameters (iJH, iJS and iJG ) for Cu " Cd and Zn sorption onto MicaK were also determined. Kinetic modeling analysis of the Elovich, pseudo-first order, pseudosecond order, intra-particle diffusion, mass transfer and intra-particle diffusivity equations using the linear coefficient of determination R2 values showed that the pseudo-second order equation was the most appropriate model for the description of Cu2+, Cd2+ and Zn2+ transport. Thus the sorption of Cu2+, Cd2+ and Zn2+ ions can be said to follow a pseudo-second order model, with chemical sorption as its rate limiting step. Experiments were also carried out to ascertain the physico-chemical properties of Mica- K. Chemical analysis revealed that the mineral is mainly comprised of Si02, MgO, Ah03 and Fe203. Physical parameters such as specific gravity, void ratio, porosity, hydraulic conductivity (at 20°C), unit weight of dry mineral, unit weight of submerged saturated mineral, unit weight of buoyant mineral, optimum moisture content (OMC), maximum dry density(MDD), and specific surface area have also been determined and reported. Elemental analyses of Mica-K have shown that; major rock-forming mineral elements comprises of AI, Fe, K, and Mg; major ore-mineral elements present include Ba, Ca, Cr, Ni and Ti; and trace elements, are Co, Mn, Cu, P,S, Si, V, B, Hg, Li, Sr and Zn. The most abundant minerals are; feldspars, chlorites, pyrites and kaolinites with dolomites, calcites and quartz being the least abundant. X-ray photoelectron spectroscopic (XPS) analysis for Cu2+, Cd2+ and Zn2+ ion-equilibrated Mica-K, demonstrated that Cu2+, Cd2+ and Zn2+_containing nodules existed on the surface of the mineral. X-Ray diffraction (XRD) studies have pointed to the possibility of formation of metal fluoride, oxide, hydroxide, carbonate and hydrogen carbonate complexes on the surface of Mica-K during metal ion adsorption. Other studies included comparative batch kinetics whereby the effects of; contact time, initial metal ion concentration, weight of mineral used, solution pH, particle size, agitation speed, temperature and nature of metal ion salt were investigated. Comparative batch equilibrium studies involved determination of the isotherms of sorption, maximum sorption level and modeling. Fixed bed experiments were performed to determine the breakthrough curves and study the sorption dynamics. The amount of Cu2+ ions adsorbed in fixed-bed experiment was greater than that of combined alkali and alkaline earth metal cations Mg2+, Ca2+, Na+ and K+ released. This indicates that ion exchange is not the only mechanism by which Cu2+ ions are removed from solution. Regeneration of sorbent for repeated use was carried out using 0.1 M HCI as the desorbing agent. The amount of copper desorbed by the acid was 27.30meq g-l (13.65 mg g") as compared to 14.26meq g-l (7.13mg g-l), copper adsorbed by Mica-K in the column. These shows that Mica-K can be regenerated effectively using weak acids. Excess amounts of acid however, can lead to the degradation of the mineral structure and thus result in the leaching of copper and other ions. Mica-K adsorbent compared quite well with a commercially available Elgalite ion exchange resin from Elga Company UK, when used to treat real water samples from different sources within Kenya and industrial effluents. It has been proven that Mica-K is a good adsorbent for both metal and non-metal ions with the amount of ion adsorbed being dependant on the type of ion, its concentration and solution pH. It is hoped that the data obtained from this research work will illustrate the importance of locally available micaceous minerals in their use as economical adsorbents of heavy metals from water and wastewater systems. It is also hoped that the results will convince the public and the decision makers of the urgent need to develop industrial and domestic uses of the locally available materials for water purification.

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