Removal Of Other Heavy Metals Research Articles

Interpretation of the adsorption process of toxic Cd2+ removal by modified sweet potato residue.

Cadmium (Cd) is a common and toxic non-essential heavy metal that must be effectively treated to reduce its threat to the environment and public health. Adsorption with an adsorbent, such as agricultural waste, is widely used to remove heavy metals from wastewater. Sweet potato, the sixth most abundant food crop worldwide, produces a large amount of waste during postharvest processing that could be used as an economic adsorbent. In this study, the feasibility of using sweet potato residue (SPR) as an adsorbent for Cd2+ adsorption was assessed. To enhance the removal rate, SPR was modified with NaOH, and the effects of the modification and adsorption conditions on the removal of Cd2+ from wastewater were investigated. The results showed that modified sweet potato residue (MSPR) could be adapted to various pH and temperatures of simulated wastewater, implying its potential for multi-faceted application. Under optimized conditions, the removal of Cd2+ by MSPR was up to 98.94% with a maximum adsorption capacity of 19.81 mg g-1. Further investigation showed that the MSPR exhibited rich functional groups, a loose surface, and a mesoporous structure, resulting in advantageous characteristics for the adsorption of Cd2+. In addition, the MSPR adsorbed Cd2+ by complexation, ion exchange, and precipitation during a monolayer chemisorption adsorption process. This work demonstrates a sustainable and environment friendly strategy for Cd2+ removal from wastewater and a simple approach for the preparation of MSPR and also revealed the adsorption mechanism of Cd2+ by MSPR, thus providing a suitable adsorbent and strategy for the removal of other heavy metals.

Sequestration of heavy metals from contaminated water using magnetic carbon nanocomposites

Heavy metals are toxic to flora, fauna and human beings. This study focused on removing toxic metals from an aqueous medium using magnetic carbon (Fe3O4@Carbon) nanocomposites. The biogenic green synthesis approach was used to fabricate the magnetic nanocomposite using low-cost poplar sawdust powder. The characterization of the nanocomposites was done using FESEM, TEM BET and FTIR. The sequestration of Pb (II), Cu (II) and Cr (VI) from water by Fe3O4@Carbon nanocomposites were studied under batch mode. The adsorption capacities for Pb (II), Cu (II) and Cr (VI) were 151.5, 48.08, and leaves49.29 mg/g respectively. The removal of metals by magnetic composites was studied in a mono, binary and tertiary network of metal ions. Adsorption isotherms studies indicated the chemosorption of Cu (II) and Cr (VI) onto the surface of nanocomposites. The thermodynamic analysis revealed that removal of studied metals ions is spontaneous and feasible. In this study, the effectiveness of magnetic nanocomposites is also explored for the removal of other heavy metals from tap water and simulated water sample. The heavy metal removal efficiency of the nanocomposites was not affected up to thrice reuse of adsorbent.

Investigations on lignite use for lead removal from aqueous solutions under static and dynamic conditions: adsorption properties and mechanism exploration

Lignite, as an abundant and low-cost material, was tested for lead (Pb(II)) removal from aqueous solutions under various experimental conditions for both static (batch) and dynamic (column) experiments. Static assays showed that Pb(II) removal efficiency increases with rising in its initial concentration, aqueous pH, and adsorbent dosage values. Adsorption kinetic and isothermal data were well fitted with the pseudo-second-order and Freundlich models, respectively, suggesting that lead removal by lignite is mainly governed by chemical processes and occurs heterogeneously on multilayer surfaces. The maximum Langmuir’s adsorption capacity was equal to 61.4 mg·g -1 , which is high in comparison to various natural materials. The laboratory column experiments showed that Pb(II) breakthrough curves and subsequent lignite adsorption efficiency is highly dependent on the bed height. Due to the short time contact between Pb(II) and lignite particles inside the column, the highest adsorption capacity was about 21%, which is lower than the one found in the batch mode. Even under dynamic conditions, lignite exhibits a high adsorption capacity compared to other adsorbents, which promotes its use as a low-cost and efficient material for Pb(II) and the removal of other heavy metals from wastewaters.

Fabrication of calcite based biocomposites for catalytic removal of heavy metals from electroplating industrial effluent

Treatment of wastewater for heavy metal removal is gaining much attention due to increase in pollution and insufficiency of water. Wastewater treatment processes is important in preventing heavy metal pollution of the receiving waters when discharged particularly from industrial effluents including electroplating industries. In this article, a novel actinobacterium Zhihengliuella sp. ISTPL4, along with different biomaterials synthesized were studied comprehensively for the removal of toxic heavy metals including Cr, Cd, Mn, Ni, Pb, Zn and Fe. Among these heavy metals, Cr(VI) being more lethal than other metal ions and present in a very high concentration of ⁓1000 mg/l in effluent of electroplating industry, pose serious health issues when enters the body. Cr(VI) reduction by the strain ISTPL4 when studied in the reactor, showed 20 % reduction of Cr(VI) to Cr(III) at an initial concentration of 1100 mg/L, along with >90 % removal of other heavy metals. The whole genome analysis of the strain showed the presence of heavy metals resistant genes and transporters, corroborating the above results. The bacterium’s adsorption capacity was then compared with synthesized biomaterials viz. only biochar, biochar with reductase enzyme, and calcined biochar with reductase enzyme. Synthesized biomaterials in the packed columns provided excellent adsorption capacity for all the heavy metals within 10–15​ min of run time and reusability potential of 5 cycles. Calcined biochar with reductase enzyme showed maximum adsorption of Cr. Langmuir isotherm and Lineweaver Burk plot best explained their adsorption mechanism and strong affinity towards heavy metals. FTIR and SEM-EDX analysis confirmed the involvement of carboxyl, hydroxyl, and amino groups in heavy metal ions’ biosorption. Furthermore, MTT assay in HepG2 showed greatest cell viability at the concentration where maximum reduction of Cr(VI) to Cr(III) occurred. We propose this current technology, which provides an excellent biosorbent in the form of calcined biocomposite with bacterial reductase enzyme for heavy metals reduction and remediation and also implementation of this technique would have great significance in wastewater treatment of metal contaminated sites.

Combined Fenton process and sulfide precipitation for removal of heavy metals from industrial wastewater: Bench and pilot scale studies focusing on in-depth thallium removal

Thallium (Tl) in industrial wastewater is a public health concern due to its extremely high toxicity. However, there has been limited research regarding Tl removal techniques and engineering practices to date. In this investigation, bench and pilot studies on advanced treatment of industrial wastewater to remove Tl to a trace level were conducted. The treatment process involved a combination of hydroxide precipitation, Fenton oxidation, and sulfide precipitation. While hydroxide precipitation was ineffective for Tl+ removal, it enabled the recovery of approximately 70%–80% of Zn as Zn hydroxide in alkaline conditions. The Fenton process provided good Tl removal (>95%) through oxidation and precipitation. Tl was then removed to trace levels (< 1.0 µg/L) via sulfide precipitation. Effective removal of other heavy metals was also achieved, with Cd< 13.4 µg/L, Cu< 39.6 µg/L, Pb< 5.32 µg/L, and Zn< 357 µg/L detected in the effluent. X-ray photoelectron spectroscopy indicated that Tl2S precipitate formed due to sulfide precipitation. Other heavy metals were removed via the formation of metal hydroxides during hydroxide precipitation and Fenton treatment, as well as via the formation of metal sulfides during sulfide precipitation. This combined process provides a scalable approach for the in-depth removal of Tl and other heavy metals from industrial wastewater.

Applicability of water-spray electric arc furnace steel slag for removal of Cd and Mn ions from aqueous solutions and industrial wastewaters

Adsorption is a fundamental process in the physicochemical treatment of wastewaters which industries employ to reduce hazardous organic and inorganic wastes in effluents. The main objective of this study is to find a suitable application of the water-spray electric arc furnace (WS-EAF) slag which is a by-product of the steelmaking process. This material was collected, crushed, milled and characterized in terms of chemical composition, morphology and phases. The results showed that the main phases of the WS-EAF slag were magnetite (Fe3O4), wustite (Fe0.94O), beta-calcium silicate (Ca2SiO4) and mayenite (Ca12Al14O33). Several parameters were applied to evaluate the performance of WS-EAF slag for removal of Cd (II) and Mn(II) from aqueous solutions and wastewaters. Adsorption kinetics of Cd and Mn ions has been discussed. The applicability of WS-EAF slag for removal of other heavy metals (Zn, Fe, Ni, Pb and Co) from wastewaters has also been examined. The best parameters to achieve 99.99 and 99.96 (%) removal for Cd and Mn ions from aqueous solutions were found to be 10 μm adsorbent particle size, 0.5 g adsorbent weight, 8 solution pH, 90 min contact time, and 10 mg/L initial metal ions concentration at room temperature. Pseudo second-order model fits well with data of Cd and Mn adsorption. The WS-EAF slag appears to be a promising material for removal of competitive heavy metals from industrial wastewater via adsorption.

REMOVAL OF Cd(II) FROM AQUEOUS SOLUTIONS BY CRUMPLED GRAPHITE OXIDE

In this study, crumpled graphite oxides (CGOs) were fabricated from graphite electrode of exhausted dry batteries (RG) by cathodic plasma electrolysis method (CPE) and applied for removing Cd(II) from aqueous solutions. The effects of pH, contact time, and initial concentrations on the removal of Cd(II) ions were studied. A removal efficiency of ∼98 % was obtained after 120 min, via the dispersion of 15 mg of CGO in Cd(II) solutions (40 mL, 1 ppm) at pH 6. The maximum adsorption capacity (qmax) was calculated to be 40.82 mg/g. Results showed that CGO is an effective adsorbent for the removal of Cd(II) from aqueous environment and acts as a promising adsorbent for the removal of other heavy metals from the polluted water.

Increase the utilisation of fly ash with electrostatic precipitation

The basic idea in this study is to look into the possibilities of reducing the heavy metal concentrations of fly ash by means of electrostatic precipitation. The utilisation of fly ash as fertiliser is hampered by its high concentrations of heavy metals, which are highly variable. Fly ash fractionation experiments were done using electrostatic precipitators at four power plants. Based on the results, the concentrations of heavy metal are at their lowest in the first collector chamber and highest in the last chamber. The concentration of cadmium in fly ash used as fertiliser can be reduced by as much as 70% by applying electrostatic precipitation fractionation. The removal of other heavy metals is not as efficient as that of cadmium. The results show that electrostatic precipitation is an adequate method in the fractionating of fly ash to be used as a fertiliser or soil amendment.

Field Study on Heavy Metal Accumulation in a Natural Wetland Receiving Acid Mine Drainage

The mechanism of surface water remediation in a natural wetland that is receiving heavy metal-rich acidic mine drainage was investigated. Selective sequential extraction was useful to derive the mechanisms of heavy metal removal in the wetland. In the upstream portion of the wetland, dissolved Fe was removed mainly as oxide-bounded mineral phases, such as hydroxides. These are important for the subsequent removal of other heavy metals. Other ion-exchangeable and carbonate-bounded heavy metals are also observed in the upstream, associated with Fe oxides. Organic matter and Fe–Mn oxides in the upstream remove Cu and Zn ions from the drainage, respectively. In the middle of portion of the wetland the removal of heavy metal ions in relatively low concentrations occurs by the emergent vegetation. Greater clay abundance and higher microbial activity of sulfate reducing bacteria in the downstream parts achieved low-level removal of metals. Multi-cell wetlands are recommended for the treatment of acidic metal bearing surface water drainage, if sufficient land area and expenses are available to construct.

Mobilization and retention of heavy metals in mill-tailings from Garpenberg sulfide mines, Sweden

The Lilla Bredsjön tailings contain less than 30% residual sulfide minerals, and an average initial content of 4% calcium carbonate. The tailings are divided into an active oxidation horizon near the surface of the tailings impoudment, an underlying intermediate horizon and a water-saturated horizon. Extensive oxidation of sulfide minerals near the tailings surface results in depletion of carbonate minerals and low pore solution pH. Following the increase of carbonate content, the leachates pH rises up to 6.5–7 at the bottom of the active oxidation horizon. The neutral conditions favour a rapid precipitation of Fe oxyhydroxides, and major removal of other heavy metals from the leachates. Fe-precipitates fill tailings integrain pores and cement tailings, modifying the permeability of the tailings matrix. As a result, Fe-precipitated layers play an important role in the formation of a barrier which restricts O 2 diffusion through the tailings, and in acting as an accumulation zone to retain heavy metals in the tailings. In addition, the shallow occurrence of the ground water level in the tailings may also contribute to the formation of the O 2 barrier. The occurrence of the barrier results in a considerable reduction of sulfide oxidation and of Fe, Cu, Zn, and SO 2 concentrations of the leachates below the Fe precipitated layers. Due to intensive weathering, clay minerals are formed in the active oxidation horizon and heavy metals are retained by clays through adsorption. The geochemical, mineralogical and geohydrological data can help to develop remedial strategies for arresting the acid mine drainage and the attendant hazardous environmental impacts.