Kinetic study of competitive CO2+ and Sr2+sorption by bauxite residue

Multi-component sorption studies are essential to identify the applicability of red mud as a low-cost sorbent for the simultaneous removal of metal ions from wastewaters. Sorption kinetics of Co2+ and Sr2+ionswas studied, at their different molar ratios in the mixture. The pseudo-second-order rate model best described the kinetics of metal sorption from binary metal systems. The increase of initial concentration of each cationin the mixture provoked its increased sorption capacity, but decreased sorption rate. Co2+sorption was superior in terms of both the rate and the capacity, therefore exertedstrong inhibitory effect on Sr2+sorption

Rapid laboratory method for the detection of chlorine in water

The possibility of chlorine detection in water by using of amperometric sensor with dialysis membrane was investigated. The sensor consists of platinum cathode and silver anode, which were immersed in electrolyte whose pH was controlled. The calibration diagrams were constructed for different electrolytes and polarization potentials. The detection limit of 0.1 mg/dm3 was obtained, middle value of sensor sensitivity was approximatelly 14 nA/mgdm'3 and response time was less than 1 s for designed amperometric sensor in laboratory conditions

Immobilization of 60Co and 90Sr ions using red mud from aluminum industry

The removal of 60Co and 90Sr from the aqueous phase was tested using red mud - the fine grained residue from bauxite ore processing. This industrial waste represents a mixture of numerous minerals, mainly oxides and hydroxides of Fe, Al, Si, and Ti. Experiments were conducted as a function of contact time, pH, and pollutant concentrations. Kinetic data were well fitted with a pseudo-second order equation. The calculated rate constants and initial sorption rates indicated faster sorption of Sr2+ ions. Removal of both cations rapidly increased with the initial pH increase from 2.5 to 3.5. With the further increase of pH, Co2+ sorption was nearly constant (98%-100%), whereas Sr2+ removal remained at the same level to initial pH ~8 and gradually increased to 100% at pH 12. Equilibrium sorption data followed the Langmuir model, with the maximum sorption capacities of 0.52 mmol/g for Co2+ and 0.31 mmol/g for Sr2+. Sorbed cations exhibited high stability in distilled water. Desorption of Co2+ was also negligible in the presence of the competing Ca2+ cation, while 42%-25% of Sr2+ ions were desorbed depending on the previously sorbed amount. The results indicate that red mud is of potential significance as Co2+ and Sr2+ immobilization agent due to its high efficiency, abundance, and low-cost. [Projekat Ministarstva nauke Republike Srbije, br. 43009

Concurrent Co2+ and Sr2+ sorption from binary mixtures using aluminum industry waste: Kinetic study

Multi-component sorption studies are essential to identify the applicability of red mud as a lowcost sorbent for the simultaneous removal of metal ions from wastewaters. Sorption kinetics of Co2+ and Sr2+ ions was investigated, at different total concentrations of mixtures and different molar ratios of two cations. Kinetics of metal sorption from binary systems was found to be well described by pseudo-second order rate model. Equilibrium sorbed amounts and equilibrium times for Co2+ sorption increased with the increase of its total concentration in the mixture, whereas pseudo-second order rate constants exhibited the opposite trend. Sr2+ sorption was strongly suppressed in the presence of Co2+ ions, and the removal efficiency decreased with increasing concentration and mole fraction of Co2+. Red mud can be used for simultaneous Co2+ and Sr2+ removal from mixtures of lower initial concentration, otherwise Co2+ sorption is dominant

Effect of experimental variables onto Co2+ and Sr2+ sorption behavior in red mud-water suspensions

The prospects of rinsed red mud (alumina production residue) utilization for liquid radioactive waste treatment have been investigated, with Co2+ and Sr2+ as model cations of radioactive elements. To evaluate the sorption effectiveness and corresponding binding mechanisms, the process was analyzed in batch conditions, by varying experimental conditions (pH, Co2+ and Sr2+ concentrations in single solutions and binary mixtures, contact time, and the concentration of competing cations and ligands common in liquid radioactive waste). Comparison of the Co2+ and Sr2+ sorption pH edges with the red mud isoelectric point has revealed that Co2+ removal took place at both positive and negative red mud surface, while Sr2+ sorption abruptly increased when the surface became negatively charged. The increase of initial cation content and pH resulted in increased equilibrium times and sorption capacity and decreased rate constants. From single metal solutions and various binary mixtures, Co2+ was sorbed more efficiently and selectively than Sr2+. While Sr2+ sorption was reduced by coexisting cations in the order Al3+ Ca2+ GT Na+ Cs+, removal of Co2+ was affected by Al3+ species and complexing agents (EDTA and citrate). Desorption of Co2+ was negligible in Ca2+ and Sr2+ containing media and in solutions with initial pH 4-7. Sr2+ desorption was generally more pronounced, especially at low pH and in the presence of Co2+. Collected macroscopic data signify that Co2+ sorption by red mud minerals occurred via strong chemical bonds, while Sr2+ was retained mainly by weaker ion-exchange or electrostatic interactions. Results indicate that the rinsed red mud represent an efficient, low-cost sorbent for Co2+ and Sr2+ immobilization

Simultaneous removal of Pb2+, Cu2+, Zn2+ and Cd2+ from highly acidic solutions using mechanochemically synthesized montmorillonite-kaolinite/TiO2 composite

The aim of the present study was to synthesize a composite of raw interstratified montmorillonite-kaolinite clay (Mt-K) with TiO2 as an additive by mechanochemical activation and investigate its usability as low-cost adsorbent for simultaneous removal of heavy metals from acidic aqueous solutions. The composite synthesized with amorphous TiO2 (TiO(2,)a) showed a significantly better removal ability of heavy metals from highly acidic solutions (pH = 2.0-4.0) compared with the Mt-K milled for an optimum period of time of 19 h (Mt-K,m) and composite synthesized with crystalline TiO2 (TiO(2,)c). As both of the composites showed the same morphologies, the same distribution of TiO2 particles on the clay matrix, the same particle size distribution (PSD) dependencies and point of zero charge (pH(PZC)) values, it has to be noticed that the difference in the adsorption behavior lies only in the different crystalline forms of the additive, i.e. TiO2 that was used for the composite preparation. It has been shown that 20% of TiO(2,)a was the optimal amount of an additive in the composite to achieve improved adsorption ability. (C) 2014 Elsevier B.V. All rights reserved

Mechanochemically improved surface properties of activated carbon cloth for the removal of As(V) from aqueous solutions

Modified activated carbon cloth is prepared by mechanochemical modification of viscose rayon carbon cloth. The effects of different milling atmospheres, in the air and inert conditions, were investigated. Changes in kind and number of acidic and basic surface groups on the surface of activated carbon cloth, upon modification, as well as before and after the sorption of arsenic were determined. Higher number of basic groups responsible for the removal of arsenic ions was achieved by modification under inert conditions. Breakage and collapse of cylindrical fibers, decrease of particle sizes, change in the shape and consistency of the particles, as well as increase of microstructural disorder i.e. the loss of turbostratic structure occurred upon milling. pHPZC values increased from 4.46 to 5.04 and 5.77 after the air and inert milling, respectively. Adsorption followed pseudo second order kinetics with chemisorption as rate-controlling step. Langmuir isotherm best fit the equilibrium data and maximum adsorption capacity is 5.5 mg g−1 at a pH value close to 7.0, typical for groundwater. The mechanism of arsenic adsorption onto activated carbon cloth milled in inert atmosphere involved electrostatic and dispersive interactions between arsenic ions and carbon particles in wide pH range (from 2 to 10)