Selective Removal Of Heavy Metals Research Articles

Selective Removal of Heavy Metals from Industrial Wastewater Using Maghemite Nanoparticle: Performance and Mechanisms

This study investigated the applicability of maghemite -Fe2O3 nanoparticles for the selective removal of toxic heavy metals from electroplating wastewater. The maghemite nanoparticles of 10 nm were synthesized using a sol-gel method and characterized by X-ray diffraction XRD and transmission electron microscopy TEM. The surface area of the nanoparticles was determined to be 198 m 2 / g using the Brunauer-Emmett-Teller method. Batch experiments were carried out to determine the adsorption kinetics and mechanisms of CrVI ,C uII, and NiII by maghemite nanoparticles. The adsorption process was found to be highly pH dependent, which made the nanoparticles selectively adsorb these three metals from wastewater. The adsorption of heavy metals reached equilibrium rapidly within 10 min and the adsorption data were well fitted with the Langmuir isotherm. Regeneration studies indicated that the maghemite nanoparticles undergoing successive adsorption-desorption processes retained original metal removal capacity. Mechanism studies using TEM, XRD, and X-ray photoelectron spectroscopy suggested that the adsorption of CrVI and CuII could be due to electrostatic attraction and ion exchange, and the adsorption of NiII could be as a result of electrostatic attraction only.

Improvement of selective removal of heavy metals in cyanobacteria by NaOH treatment

In the freshwater cyanobacterium, Tolypothrix tenuis, treatment with 0.1 M NaOH increased its Cd-selective adsorption ability in the presence of Ca(2+) or Mg(2+). The selective adsorption was also achieved by other alkaline treatments. Energy-distributed spectroscopy analysis revealed that Cd(2+) was found mainly on the surface of non-treated cells, whereas it was distributed throughout the cell after NaOH treatment. The alkaline treatment was effective in increasing the selective adsorption ability of the cyanobacterium for other bivalent heavy metals such as Cu(2+), Pb(2+) and Zn(2+). The treatment was also applicable to Anabaena variabilis and Microcystis aeruginosa, which are typical cyanobacteria causing algal blooms. The main binding site of Cd(2+) in NaOH-treated cells is assumed to be the carboxyl groups because the binding ability of the cells was diminished by the esterification of carboxyl groups. These results suggest that alkaline treatment of cyanobacteria is a useful technique for producing biosorbents having highly specific binding abilities for heavy metals.

Membrane Contactors in Industrial Applications

In a membrane contactor the membrane separation is completely integrated with a conventional phase contacting operation like extraction or absorption. In this way the benefits of both technologies can be fully exploited. The membrane contactor technology is a new technology. The first full scale membrane contactor installations that have been installed in industry are running successfully for some years now. Industrial applications of membrane contactors, including aromatics recovery from a process water, selective removal of heavy metals from a galvanic process bath and ammonia product recovery from an off gas stream, are discussed. Membrane contactors are of interest for the chemical, petrochemical, pharmaceutical and galvanic industry for both water and gas treatment as end of pipe technology but also for product recovery and as integrated process solution. New applications under development—CO2 membrane gas absorption and pertraction for produced water treatment—are discussed technically and economically to show the wide scope of the technology.

Ion Exchange Extraction of Heavy Metals from Wastewater Sludges

Heavy metals are common contaminants of some industrial wastewater. They find their way to municipal wastewaters due to industrial discharges into the sewerage system or through household chemicals. The most common heavy metals found in wastewaters are lead, copper, nickel, cadmium, zinc, mercury, arsenic, and chromium. Such metals are toxic and pose serious threats to the environment and public health. In recent years, the ion exchange process has been increasingly used for the removal of heavy metals or the recovery of precious metals. It is a versatile separation process with the potential for broad applications in the water and wastewater treatment field. This article summarizes the results obtained from a laboratory study on the removal of heavy metals from municipal wastewater sludges obtained from Ardhiya plant in Kuwait. Data on heavy metal content of the wastewater and sludge samples collected from the plant are presented. The results obtained from laboratory experiments using a commercially available ion exchange resin to remove heavy metals from sludge were discussed. A technique was developed to solubilize such heavy metals from the sludge for subsequent treatment by the ion exchange process. The results showed high efficiency of extraction, almost 99.9%, of heavy metals in the concentration range found in wastewater effluents and sludges. Selective removal of heavy metals from a contaminated wastewater/sludge combines the benefits of being economically prudent and providing the possibility of reuse/recycle of the treated wastewater effluents and sludges.

The membrane contactor: Environmental applications and possibilities

AbstractIn a membrane contactor, separation is fully integrated with another separation technology, such as extraction or absorption, in order to fully exploit the benefits of both technologies. Membrane contactor applications can be found in both water and gas treatment. Several recently developed industrial applications—aromatics recovery from a process water, selective removal of heavy metals from a galvanic process bath, and ammonia recovery from an off gas stream—will be discussed from both technical and economic perspectives to show the wide scope of the technology.

REVERSE POTENTIAL PHENOMENA IN THE MEMBRANE-ELECTRODE (M-E) PROCESS

Conventional water treatment techniques typically suffer from severe limitations in selective removal and recovery of heavy metals from dilute solutions. For instance, treatment by pH control, chemical reduction, and chemical oxidation result in precipitation of heavy metaJs, which are subsequently landfilled. Ion exchange suffers from lack of selectivity in cation removal from multi-component mixtures, while electrochemical reduction has severe limitations in dilute solutions. In order to address the problem of selective heavy metal removal and recovery, development of the Membrane-Electrode (M-E) process was undertaken. The M-E process is a hybrid of electrochemical reduction and ion-exchange technologies and permits selective ion-exchange from dilute aqueous solutions. High cation selectivities in the M-E process is due to controlled rate of ion-exchange. It has been discovered that cation exchange rates can be controlled by application of an electrical potential difference (pd), and that an inverse relationship exists between pd and the rate of ion-exchange. This behavior is termed as the “Reverse-Potential Phenomena”. Typically, the rate of ion-exchange in conventional ion-exchange processes is dependent upon the cation concentration in solution, and cation loading on the ion-exchange material; this rate cannot be controlled by external means. Thus far, the M-E process has been effectively demonstrated for selective recovery of Pb2+ and Cu2+ ions from dilute aqueous binary and ternary cation solutions [,]. This paper focuses on the effect of Reverse-Potential phenomena on selectivity in the Cu2+ and Ni2+ binary solution mixture.

Heavy-metal separation from sludge using chelating ion exchangers with nontraditional morphology

Solid-phase wastes or hazardous waste sites containing heavy metals are a major environmental concenr due to the toxicity characteristic of the heavy metal. Generally, in such cases the heavy metals constitute a small fraction (usually < 5%) of the solid phase, the rest being a background of innocuous nontoxic materials which are not important from a regulatory point. Therefore, the best treatment scheme would be one which achieves selective removal of the heavy metals, leaving the remainin solid phase as nontoxic. This problem of selective removal is compounded by the fact that the nontoxic background materials may interact with the heavy metals through generation of high buffer capacity, ion exchange, complexation, etc. Since these interactions may occur independent of each other, any process conceived to address this situation should be versatile enough to be effective for all of the above-mentioned cases. Ion-exchange technology has been proven to be successful in selectively removing heavy-metal ions from solution, but cannot be used directly in a high suspended solids waste scenario. This study explores the use of a material termed ‘composite ion-exchange material (CIM)’. During the last five years, extensive studies were carried out to validate the suitability of this material CIM in selectively removing heavy metals from a background solid phase mostly containing innocuous materials. This communication presents the key findings of cases where the morphology of this material — in combination with tailoring of the chemistry within the suspended solids reactor, or with an electric-gradient-induced ion-movement phenomenon — can be used advantageously in effecting selective and reversible removal of heavy metals from such an unfavorable background sludge.

Selective Removal of Heavy Metals from Industrial Dusts, Fly Ashes and Process Waste Waters by Carrier Extraction

Selective recovery and recycling of heavy metals from solid wastes and process waste waters by solvent extraction and liquid membrane technique are reviewed by presenting typical examples, which cover metal recovery from hydroxyl sludges, metal dusts, fly ashes of incinerators. Furthermore, metal recovery from the process waste waters, especially from viscose production, as well as from pickling and electrowinning baths, leaching residues, effluents of fur finishing industry are covered. It is shown, that no generally applicable strategy exists. For each recovery process, the particular steps of the selective recovery as well as their succession have to be optimized.

Selective removal of heavy metals from contaminated kaolin by chelators

The competitive desorption/dissolution of kaolin-adsorbed heavy metal mixtures and mixtures of adsorbed Cd with Mg and/or Ca by four chelators (NTA, EDTA, EGTA, and DCyTA) was investigated. Metals were adsorbed on kaolin at pH 7 and the effects of chelator type and concentration on the extent of metal dissolution was studied at a solution pH of 10. EGTA addition. EGTA was the most effective chelator in selectively removing Cd from kaolin in the presence of adsorbed alkaline-earth metals. Approximately 90% of the adsorbed Ca and Mg were retained on the kaolin until almost all (> 80%) of the cadmium was dissolved by EGTA chelator. NTA was the least effective chelator in selectively dissolving Cd from kaolin contaminated with both Cd and Ca (≈ 45% of the adsorbed Cd could not be removed). All four chelators exhibited some desorption/dissolution selectivity for Cd, Cu, and Pb adsorbed on kaolin. When the concentration of chelator in solution was insufficient to dissolve all adsorbed metals, the observed metal ordering for chelation and dissolution was Cd > Cu > Pb (for EGTA), Cd > Pb > Cu (for EDTA and DCyTA), and Cu > Cd > Pb (for NTA).

Solid Phase Heavy Metal Separation Using Composite Ion-Exchange Membranes

ABSTRACT Selective removal of heavy metals from sludges or soil is a challenging problem because the heavy metals constitute a small fraction (usually <5%) of the solid phase, the rest being a background of innocuous non-toxic materials which are not important from a regulatory viewpoint. However, the non-toxic background materials may interact with the heavy metals through generation of high buffer capacity, ion-exchange, complexation, etc., thus compounding the problem. This study explores the feasibility of using composite ion-exchange membranes under such unfavorable conditions. This paper also reports on aspects of tailoring the chemistry within the sludge reactor to get optimum results.

Renal tubular secretion of the alkanesulfonate 2,3-dimercapto-1-propanesulfonate.

The in vivo tubular secretion and metabolism of 2,3-dimercapto-1-propanesulfonate (DMPS) was examined in the chicken by use of the Sperber technique. Infusion of DMPS into the renal portal circulation of the chicken at rates equal to or less than 7.5 mumol X min-1 X kg body wt-1, resulted in a tubular excretion ratio of 0.5 for DMPS with 90% of the infused DMPS excreted in the urine unchanged. Renal tubular secretion accounted for approximately 90% of the total DMPS excreted into the urine during the infusion of DMPS at a rate of 0.75 mumol X min-1 X kg-1. The secretion of DMPS was saturable and was inhibited by p-aminohippurate (PAH), probenecid, and heptanesulfonate. Taurine (2-aminoethanesulfonate), isethionate (2-hydroxyethanesulfonate), and 2-mercaptoethanesulfonate had no effect on the secretion of DMPS or PAH. Renal tubular secretion may explain several pharmacological characteristics previously reported for DMPS, including the selective removal of heavy metals from the kidney.