Heavy metal removing by modified bentonite and study of catalytic activity

Removal of the Highly Toxic Anticoccidial Monensin Using Six Different Low-Cost Bio-Adsorbents

The anticoccidial monensin (MON) is a high-concern emerging pollutant. This research focused on six low-cost bio-adsorbents (alfa, cactus, and palm fibers, and acacia, eucalyptus, and zean oak barks), assessing their potential for MON removal. Batch adsorption/desorption tests were carried out, and the results were fitted to the Freundlich, Langmuir, Linear, Sips, and Temkin models. The concentrations adsorbed by the six materials were very similar when low doses of antibiotic were added, while they differed when adding MON concentrations higher than 20 µmol L-1 (adsorption ranging 256.98-1123.98 μmol kg-1). The highest adsorption corresponded to the sorbents with the most acidic pH (<5.5) and the highest organic matter and effective cation exchange capacity values (eucalyptus bark and acacia bark, reaching 92.3% and 87.8%), whereas cactus and palm fibers showed the lowest values (18.3% and 10.17%). MON desorption was below 8.5%, except for cactus and palm fibers. Temkin was the model showing the best adjustment to the experimental data, followed by the Langmuir and the Sips models. The overall results indicate that eucalyptus bark, alfa fiber, and acacia bark are efficient bio-adsorbents with potential for MON removal, retaining it when spread in environmental compartments, reducing related risks for human and environmental health.

Experimental and Molecular Dynamics Simulation Insights into Adsorption of Co(II), Cr(III), and Cu(II) on Chitosan and Chitosan/Tripolyphosphate Nanoparticles

Chitosan (CS)/tripolyphosphate (TPP) nanoparticles were synthesized using the ionic gelation method based on the mass ratio and volume ratio between CS and TPP and then subsequently characterized using XRD, FT-IR, and SEM. The interaction between the metal ions Co(II), Cr(III), and Cu(II) on CS and 2CS/TPP was simulated using molecular dynamics (MD), and the findings were compared with the experimental data. CS/TPP nanoparticles were more favorable than using pure chitosan at a % removal efficiency of 91.47, 89.11, and 78.11 for Cu(II), Cr(III), and Co(II), respectively. The binding energy between 2CS/TPP and the metals was more favorable than that for CS at -214.95, -106.87, and -58.11 kcal/mol for Cr(III), Co(II), and Cu(II), respectively. The CS/TPP nanoparticles greatly affect metal adsorption and are therefore considered materials for wastewater treatment.

Synthesis of magnetic bentonite-gelatin hydrogel beads and their applications in Cu2+ capturing

Heavy metal ions that exist in groundwater and farmland jeopardize the ecological environment and are very difficult to remove because of the complicated actual environment. Raw bentonite-gelatin beads (RB-GT) and magnetic bentonite-gelatin beads (MB-GT) synthesized in this work would be an appropriate tool to solve this problem. Those beads are synthesized by a facile hybrid injection method. Their adsorption behaviors on Cu(II) ions were systematically investigated using the batch adsorption method. The beads were characterized by scan electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS). The adsorption isotherm and adsorption kinetic study showed that the Cu2+ adsorption by MB-GT beads fitted the Langmuir model and the pseudo-second model. The adsorption maximum capacities reached 192.5 mg/g and 236.5 mg/g with Cu concentration of 1000 mg/L for RB-GT and MB-GT beads, respectively. The competitive adsorption with other heavy metal ions (Ni(II), Pd(II) and Cd(II)) were compared. The adsorption of Cu(II) mechanisms is also further discussed.

Assessment of the Levels of Potentially Toxic Elements Contained in Natural Bentonites Collected from Quarries in Turkey

Potentially toxic elements (PTEs) are an important type of pollutant, causing constant and far-reaching concerns around the world due to their increase in the mining process. Bentonite formed by the alteration of glass-rich volcanic rocks is a smectite clay consisting mostly of montmorillonite. Bentonite is an important mineral used in a wide range of applications in many fields such as oil and gas, agriculture, food, pharmacological, cosmetic, and construction industries due to its unique qualities. Given the widespread distribution of bentonite in nature and its use in a wide variety of consumer products, it is inevitable that the general population will be exposed to PTEs contained in bentonites. In this study, concentrations of PTEs in 69 bentonite samples collected from quarries located in different geographical regions of Turkey were analyzed by an energy-dispersive X-ray fluorescence spectrometric method. The average concentrations of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Zr, and Pb in bentonite samples were found to be 3510, 95, 129, 741, 30,569, 67, 168, 25, 62, 9, 173, and 28 mg/kg dry weight, respectively. Results of the enrichment factor relating to Earth's crust average indicated moderate enrichment with Cr, Ni, and Pb and significant enrichment with Co and As.

Synthesis of Zeolites from Fine-Grained Perlite and Their Application as Sorbents

The hydrothermal alteration of perlite into zeolites was studied using a two-step approach. Firstly, perlite powder was transformed into Na-P1 (GIS) or hydro(xy)sodalite (SOD) zeolites at 100 °C and 24 h using 2 or 5 M NaOH solutions. Secondly, the Si:Al molar ratio of the reacted Si-rich solution was adjusted to 1 by Na-aluminate addition to produce zeolite A (LTA) at 65 or 95 °C and 6 or 24 h at an efficiency of 90 ± 9% for Al and 93 ± 6% for Si conversion. The performance of these zeolites for metal ion removal and water softening applications was assessed by sorption experiments using an artificial waste solution containing 4 mmol/L of metal ions (Me²⁺: Ca²⁺, Mg²⁺, Ba²⁺ and Zn²⁺) and local tap water (2.1 mmol/L Ca²⁺ and 0.6 mmol/L Mg²⁺) at 25 °C. The removal capacity of the LTA-zeolite ranged from 2.69 to 2.86 mmol/g for Me²⁺ (=240–275 mg/g), which is similar to commercial zeolite A (2.73 mmol/g) and GIS-zeolite (2.69 mmol/g), and significantly higher compared to the perlite powder (0.56 mmol/g) and SOD-zeolite (0.88 mmol/g). The best-performing LTA-zeolite removed 99.8% Ca²⁺ and 93.4% Mg²⁺ from tap water. Our results demonstrate the applicability of the LTA-zeolites from perlite for water treatment and softening applications.

Adsorption mechanism of Pb2+ in montmorillonite nanopore under various temperatures and concentrations

Adsorption of lead (Pb²⁺) onto the montmorillonite (Mt) surface is one of the key approaches to remove Pb²⁺ in geological and environmental engineering. Temperature and initial Pb²⁺ concentration are two essential factors that influence the adsorption capacity of Mt on absorbing Pb²⁺. However, the nanoscale governing mechanism of temperature and initial concentration on Pb²⁺ adsorbing of Mt is still unclear. This research performed comprehensively molecular dynamics (MD) simulations to investigate how temperature and initial concentration affect the dynamic Pb²⁺ adsorption of Mt nanopore. The Pb²⁺ removal ratio shows a two-stage variation with the increase of initial Pb²⁺ concentration. Temperature controls the maximum initial Pb²⁺ concentration for complete Pb²⁺ removal by changing the maximum adsorption energy of Mt. Temperature also influences the maximum adsorption capacity and Pb²⁺ removal ratio of Mt nanopore indirectly by changing diffusion and hydration state of Pb²⁺. The initial Pb²⁺ concentration corresponding to the maximum adsorption energy coincides with the maximum initial Pb²⁺ concentration determined by the Pb²⁺ removal ratio. Lower adsorption energy and higher level of hydration and diffusion make Pb²⁺ absorbing on Mt surface become more difficult, reducing the Pb²⁺ adsorbing capacity of Mt. The initial Pb²⁺ concentration influences adsorption capacity and Pb²⁺ removal ratio not only via altering the quantity of Pb²⁺ but also through controlling the adsorption energy of Mt, as well as the diffusion and hydration state of Pb²⁺. With the increase of initial Pb²⁺ concentration, the hydration of Pb²⁺ is weakened while the adsorption energy of Mt and diffusion of Pb²⁺ are enhanced.

Preparation and application of Fe3O4@Acetamidoxanthate as a unique nanosorbent in heavy metal removing

Chelating agents are one of the most important substances in metal extraction, but separation is the main problem in the use of these agents as an adsorbent. After the adsorption of metals by an external magnet, magnetic NPs provide the possibility of easy collecting and isolating the adsorbent nanomaterial for many applications. Given the immense importance of magnetic NPs, there has been widespread interest in accessing the above adsorbent. In the present study, an attempt was made to synthesize acetamido xanthate which was coupled to NPs and has the potential to be used as a nano-adsorbent for the removal of heavy metals. This novel nano sorbent was characterized by scanning electron microscopy (SEM), Fourier transforms infrared (FT-IR), and Nuclear Magnetic Resonance (NMR) spectroscopy. The effect of some parameters such as temperature, time, pH, and the amount of adsorbent on the extraction reaction was investigated. The optimized condition for extraction of cerium was temperature of 30°C, pH = 8, reaction time of 45 minutes using 7.5 mg of the prepared nanosorbent, that in such condition the yield of reaction achieved up to 97%. The prepared adsorbent showed high efficiency in the adsorption of heavy metals specifically.

A technology review on treatment of acid mine drainage with bentonite–steel slag composite

Acid mine drainage (AMD) which produced in the process of mining seriously pollutes the water resources and endangers the ecological environment due to its physicochemical characteristics, such as low pH, high salinity and high heavy metal concentrations. In recent decades, the treatment of AMD has become a key issue in the field of environmental protection. One important method of AMD treatment is adsorption method, and the selection of adsorbent is the key of this technique. Bentonite and steel slag are usually sintered at high temperatures to prepare bentonite–steel slag composite. AMD treatment with bentonite–steel slag composite, as a new adsorbent, is emerging as a promising treatment method by physical adsorption, ion exchange and chemical neutralization. The bentonite–steel slag composites mainly include bicomponent composite with bentonite–steel slag and multicomponent composite with bentonite–steel slag modifier. The author found that this important research question was rarely paid attention to, therefore, and the author combined with previous research and theories to promote the explanation of this problem. In this review, the technology of treatment of AMD with bentonite–steel slag composite is comprehensively discussed. Also, the role of its mechanism is also discussed in-depth. This paper provides a scientific reference on the remediation of contaminated environments.

Removal of cadmium and lead from aqueous solutions by thermal activated electrolytic manganese residues

Electrolytic manganese residues (EMR) is produced from the electrolysis manganese industry. In this study, the thermal activated EMRs (T-EMR) were used to adsorb cadmium and lead from aqueous solution. X-ray diffractometer (XRD), scanning electron microscope-Energy Dispersive Spectrometer (SEM-EDS), X-ray photoelectron spectroscopy (XPS) were adopted to characterize EMR before and after the modification, and the performance and adsorption mechanisms of T-EMR for cadmium and lead were determined. Results show that the pH has a strong influence on the adsorption of cadmium and lead and the maximum adsorption capacity can be achieved at pH 6. The adsorption of Cd(II) can be better fitted by the Lagergren pseudo-first-order dynamic model, while that of Pb(II) fits the pseudo-second-order kinetic model better. The Freundlich isotherm model fits the adsorption of two metals better than Langmuir model. The thermodynamic results demonstrate that the adsorption of Cd(II) or Pb(II) on T-EMR is endothermic and spontaneous. As the nitric acid with pH 0.5 was used, nearly all of the adsorbed Cd(II) and 75% Pb(II) can be desorbed from the loaded T-EMR. It is concluded that the adsorption of Cd(II) and Pb(II) on T-EMR is in virtue of electrostatic attraction, ion-exchange and surface precipitation. The heavy metals are mainly adsorbed on ferric and manganese oxides and silicate minerals in T-EMR by electrostatic attraction. In addition, cadmium and lead also can be adsorbed via the ion exchange reaction. Moreover, some Pb(II) are adsorbed by forming lead sulfate. Thus, T-EMR may be an environmentally-friendly, effective adsorbent for the removal of heavy metals from aqueous solution.

Removal of Barium from Solution by Natural and Iron(III) Oxide-Modified Allophane, Beidellite and Zeolite Adsorbents

Efficient capture of barium (Ba) from solution is a serious task in environmental protection and remediation. Herein, the capacity and the mechanism of Ba adsorption by natural and iron(III) oxide (FeO) modified allophane (ALO), beidellite (BEI) and zeolite (ZEO) were investigated by considering the effects of contact time, temperature, pH, Ba2+ concentration, adsorbent dosage, the presence of competitive ions and adsorption-desorption cycles (regenerability). Physicochemical and mineralogical properties of the adsorbents were characterized by XRD, FTIR, SEM with EDX and N2 physisorption techniques. The Ba2+ adsorption fitted to a pseudo-first-order reaction kinetics, where equilibrium conditions were reached within <30 min. BEI, ALO and ZEO with(out) FeO-modification yielded removal efficiencies for Ba2+ of up to 99.9%, 97% and 22% at optimum pH (pH 7.5-8.0). Adsorption isotherms fitted to the Langmuir model, which revealed the highest adsorption capacities for BEI and FeO-BEI (44.8 mg/g and 38.6 mg/g at 313 K). Preferential ion uptake followed in the order: Ba2+ > K+ > Ca2+ >> Mg2+ for all adsorbents; however, BEI and FeO-BEI showed the highest selectivity for Ba2+ among all materials tested. Barium removal from solution was governed by physical adsorption besides ion exchange, intercalation, surface complexation and precipitation, depending mainly on the absorbent type and operational conditions. BEI and FeO-BEI showed a high regenerability (>70-80% desorption efficiency after 5 cycles) and could be considered as efficient sorbent materials for wastewater clean-up.