Application of raw and modified clay for the removal of heavy metals from aqueous solutions

This work represents a fundamental study of the simultaneous sorption of heavy metals from aqueous solutions by locally available raw and mechanochemically activated natural clay. The obtained results show that the investigated clay, as an economical and efficient sorbent, has potential for application in the treatment of heavy-metal-contaminated wastewaters

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)

Hydrogen desorption from vacant MgH2

The hydrogen desorption properties of vacant MgH2 structure were investigated both experimentally and theoretically. Ion irradiation by Ar8+ and Xe8+ ions were used to induce structural changes in MgH2. Hydrogen desorption properties were investigated by temperature programmed desorption (TPD). To obtained deeper insight in structural changes during desorption theoretical calculations were performed using DFT approach within Abinit code. Results showed that there are several mechanisms involved in desorption process, which depend on defect concentration, their position and their interaction and ordering. It has been demonstrated that the changes in near-surface area play the crucial role in desorption kinetics

Removal of pertechnetate from aqueous solution using activated pyrolytic rubber char

Low-cost adsorbents, synthesized by pyrolysis of waste rubber (CR) and activated with KOH (CRA), have shown the high removal ability of from aqueous solutions in wide range of pHs (2-10) with fast adsorption rate. The Langmuir and Freundlich models suggests monolayer and multilayer adsorption of onto CR and CRA surface, respectively. The removal mechanism of from solution occurs by replacement with OH- from surface groups (phenolic and/or accompanying carboxylic) of CR and CRA indicating anion exchange mechanism

Mechanism of sorption of pertechnetate onto ordered mesoporous carbon

Ordered mesoporous carbon (OMC) was used as an adsorbent for the removal of pertechnetate (TcO4 (-)) anion. The maximum uptake (93 %) of TcO4 (-) was obtained after 60 min of contact. The adsorption of TcO4 (-) is almost pH-independent in very wide pH region (from 4.0 to 10.0). Maximum K (d) of 6.6 x 10(3) cm(3) g(-1) was found at pH 2.0. TcO4 (-) interacts with carboxylic functional groups present at the surface of the OMC by displacing the OH- ions with TcO4 (-) via ion exchange mechanism

The potential of ball-milled Serbian natural clay for removal of heavy metal contaminants from wastewaters: Simultaneous sorption of Ni, Cr, Cd and Pb ions

The influence of mechanical milling of natural Serbian clay on removal of heavy metals from an aqueous medium was investigated. The simultaneous sorption of the 4 toxic heavy metals (Ni, Cr, Cd and Pb), which are often present together in numerous polluting spills and in agrochemicals was evaluated. Microstructural and morphological changes in the ball-milled clay were characterized by X-ray diffraction (XRD), particle size distribution (PSD) and scanning electron microscopy (SEM). Induced changes in microstructure were correlated to the cation exchange capacity (CEC), determined by the EPA Method 9081. The CEC value has increased from 77 meq/100 g for the unmilled clay, to 95 meq/100 g for the milled clay. Regarding the untreated clay, the cation competition reveal some differences in their sorption: complete sorption (about 98% of the initial concentration) was achieved for Cr and Pb, while about 19% of the initial concentration of Cd and Ni still persist in the solution. The order of affinity of the metal ions is Pb approximate to Cr GT Cd approximate to Ni and it has not changed upon milling. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Hydrogen desorption properties of MgH2 catalysed with NaNH2

To improve hydrogen desorption properties of MgH2, mechanical milling of MgH2 with low concentration (2 and 5%) of NaNH2 has been performed. Pre-milling of MgH2 for 10 h has been done and then six samples have been synthesised with different milling times from 15 to 60 min. Microstructural characterisation has been performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser scattering measurements (PSD), and correlated to desorption properties examined using Differential Scanning Calorimetry (DSC) and Hydrogen Sorption Analyser (HSA). Thermal analysis shows that desorption temperatures are shifted towards lower values. It also highlights the significance of milling time and additive concentration on desorption behaviour. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Influence of ageing of milled clay and its composite with TiO2 on the heavy metal adsorption characteristics

The aim of the present study was to investigate the effect of ageing of mechanochemically synthesized clay and its TiO2 composite on the simultaneous removal of Pb(II), Cd(II), Cu(II) and Zn(II) ions from acidic aqueous solutions. The effect of different ageing times on sorption behavior of 1, 2, 10 and 19 h milled clays, as well as the clay composite with 20 wt% of amorphous TiO2 (TiO2,a), was investigated. Ageing of the milled clays has stronger influence on the removal of Zn(II) and Cd(II) than on the removal of Pb(II) and Cu(1) ions. Ageing is particularly pronounced for the samples milled for 1, 2 and 10 h (which lost enhanced sorption properties after 3 months of ageing), and less pronounced for the samples milled longer period of time, 19 h (which retained sorption properties until 6 months). After these periods of time sorption capacities became nearly the same as the sorption capacities of the raw (unmilled) clay. The different responses on the ageing process of milled clays and composite are a consequence of microstructural changes such as recrystallization of montmorillonite phase and decrease in particle sizes. Slower ageing of composite compare to the milled clays can be related to the stabilization effect of TiO2 particles which are dispersed in the clay matrix thus preventing recrystallization of the sample particles. Only a slight tendency towards the formation of agglomerations was noticed after 12 months of ageing. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved

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

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

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