Hikaru Sawai

Effect of Extraction Variables on the Biodegradable Chelant-Assisted Removal of Toxic Metals from Artificially Contaminated European Reference Soils

Development of aminopolycarboxylate chelants (APCs) having enhanced biodegradability is gaining increasing focus to replace the EDTA and its homologs with those used widely for the ex situ treatment of contaminated soils and are potential eco-threats. The paper reports the chelant-assisted extraction of the toxic metals (Cd, Cu, Pb, and Zn) from the metal-spiked European reference soils (Eurosoil 1 and Eurosoil 4) using biodegradable APCs, namely EDDS, GLDA, and HIDS. The effects of chelant-to-metal molar ratio, solution pH, and metal/chelant stability constants were evaluated, and compared with that of EDTA. The selectivity aptitude of the biodegradable chelants towards the toxic metals was assumed from the speciation calculations, and a proportionate correlation was observed at neutral pH. Pre- and post-extractive solid phase distributions of the target metals were defined using the sequential extraction procedure and dissolution of metals from the theoretically immobilized fraction was witnessed. The effect of competing species (Al, Ca, Fe, Mg, and Mn) concentrations was proven to be minimized with an excess of chelant in solution. The highlight of the outcomes is the superior decontamination ability of GLDA, a biodegradable APC, at minimum chelant concentration in solution and applicability at a wide range of pH environments.

Decontamination of spent iron-oxide coated sand from filters used in arsenic removal

Sand filters devised with iron-rich adsorbents are extensively promoted and deployed in the arsenic-prone south and south-east Asian countries (e.g., Bangladesh). The approach offers superior performance in removing arsenic while the spent sludge from the sand filters is an issue of concern due to the possibility of toxic releases after being discarded. In this work, a new technique is proposed for the treatment of spent iron-oxide coated sand (IOCS) from filters used in arsenic removal. Chelant-washing of the arsenic-loaded IOCS is combined with the solid phase extraction treatment to accomplish the objective. The unique point of the proposed process is the cost-effective scheme, which includes the option of recycling of the washing solvent beside the decontamination of the spent arsenic-rich sludge.

Chelant-induced reclamation of indium from the spent liquid crystal display panels with the aid of microwave irradiation.

Indium is a rare metal that is mostly consumed as indium tin oxide (ITO) in the fabrication process of liquid crystal display (LCD) panels. The spent LCD panels, termed as LCD-waste hereafter, is an increasing contributor of electronic waste burden worldwide and can be an impending secondary source of indium. The present work reports a new technique for the reclamation of indium from the unground LCD-waste using aminopolycarboxylate chelants (APCs) as the solvent in a hyperbaric environment and at a high-temperature. Microwave irradiation was used to create the desired system conditions, and a substantial abstraction of indium (≥80%) from the LCD-waste with the APCs (EDTA or NTA) was attained in the acidic pH region (up to pH 5) at the temperature of ≥120 °C and the pressure of ~50 bar. The unique point of the reported process is the almost quantitative recovery of indium from the LCD-waste that ensured via the combination of the reaction facilitatory effect of microwave exposure and the metal extraction capability of APCs. A method for the selective isolation of indium from the extractant solution and recycle of the chelant in solution is also described.

Chelant-Assisted Depollution of Metal-Contaminated Fe-Coated Sands and Subsequent Recovery of the Chemicals Using Solid-Phase Extraction Systems

The disposal of potentially toxic element (PTE)-loaded sludge that is produced during industrial or commercial wastewater treatments evoke concerns because of the probability of hazardous environmental consequences. In the current work, we proposed a chelant-assisted decontamination technique of the laboratory-produced PTE-loaded (As, Cd, Pb) polymeric-Fe-coated sludge and subsequent recovery of the chelants and PTEs. The chelant options include both biodegradable (EDDS, GLDA, and HIDS) and non-biodegradable (EDTA) alternatives. The washing performance was compared and discussed in terms of the solution pH and relative stabilities of the complexes of PTEs and chelants in solution. The changes in solution pH or chelants have no significant effect on the chelant-induced removal efficiency of Cd, and the same result was observed for Pb at extreme and moderate acidic pH. The As-extraction rate is also improved with chelant in the solution despite a limited interaction between the chelant and the arsenic species in the solution. The column-packed solid-phase extraction (SPE) system, which was equipped with macrocycle, chelating resin, or ion-exchange resin, was used to explore the corresponding separation performance of the PTEs and chelant. The macrocycle-equipped SPE system shows better selectivity than other SPEs in terms of extraction and recovery performance of the PTEs regardless of the chelants. Some unique points of the proposed process are minimum environmental burden due to the use of biodegradable materials in the washing solution and cost minimization by recycling the ingredients.

Chemical-Induced Washing Remediation of Metal-Contaminated Soils

The immobilization or removal of toxic components using aqueous extractants, with or without additives, is one of the commonly practiced techniques for the treatment of metal-contaminated soils. However, rather than the use of water alone, the solution with chemical-additives is preferred due to the less time requirement and better separation effectiveness. There is a long-favored list of additives that have been used for the chemical-induced washing remediation of soils, which include acids, bases, chelants, surfactants, and so forth. The objective of this chapter is to provide a brief overview of the chemical-assisted soil washing approaches.

Liquid electrode plasma-optical emission spectrometry combined with solid-phase preconcentration for on-site analysis of lead

A relatively rapid and precise method is presented for the determination of lead in aqueous matrix. The method consists of analyte quantitation using the liquid electrode plasma-optical emission spectrometry (LEP-OES) coupled with selective separation/preconcentration by solid-phase extraction (SPE). The impact of operating variables on the retention of lead in SPEs such as pH, flow rate of the sample solution; type, volume, flow rate of the eluent; and matrix effects were investigated. Selective SPE-separation/preconcentration minimized the interfering effect due to manganese in solution and limitations in lead-detection in low-concentration samples by LEP-OES. The LEP-OES operating parameters such as the electrical conductivity of sample solution; applied voltage; on-time, off-time, pulse count for applied voltage; number of measurements; and matrix effects have also been optimized to obtain a distinct peak for the lead at λmax=405.8nm. The limit of detection (3σ) and the limit of quantification (10σ) for lead determination using the technique were found as 1.9 and 6.5ng mL-1, respectively. The precision, as relative standard deviation, was lower than 5% at 0.1μg mL-1 Pb, and the preconcentration factor was found to be 187. The proposed method was applied to the analysis of lead contents in the natural aqueous matrix (recovery rate:>95%). The method accuracy was verified using certified reference material of wastewaters: SPS-WW1 and ERM-CA713. The results from LEP-OES were in good agreement with inductively coupled plasma optical emission spectrometry measurements of the same samples. The application of the method is rapid (≤5min, without preconcentration) with a reliable detection limit at trace levels.

Solidification/Stabilization: A Remedial Option for Metal-Contaminated Soils

Decontamination of hazardous discards by immobilization of toxic components is a longstanding approach for managing waste, while it gained much attention in recent years due to the increasing number of statutes and regulations favouring the technology. The solidification/stabilization (S/S) technique is the commonly adopted immobilization option to treat the contaminated soils, which employ additives to convert the hazardous waste to non-hazardous mass in accordance with the legitimate landfill provisions. The discussion is further extended to the stabilization of toxic elements in contaminated soils using chemical amendments. The current paper presents a summarized overview on the application of S/S technique in managing metal-contaminated soil, including information about the frequently used additives for the purpose, and the steps involved in the implementation of S/S remediation.

Environmental hazards associated with open-beach breaking of end-of-life ships: a review

End-of-life (EOL) ships contribute significantly to the flow of recycled industrial Fe and non-Fe metal materials in resource-poor developing countries. The ship scrapping (breaking) and recycling industry (SBRI) recycles 90–95% of the total weight of EOL ships and is currently concentrated in Bangladesh, India, Pakistan, Turkey, and China, due to the high demand for recyclable and reusable materials there, an abundance of low-cost labor, and lenient environmental regulations. However, the SBRI has long been criticized for non-compliance with standards relating to occupational health, labor safety, and to the management of hazardous materials. Among the different EOL recycling options, Bangladesh, India, and Pakistan use open beaching, a technique that exposes all spheres of the environment to the release of hazardous materials from EOL ships. This article summarizes the current state of knowledge on the environmental exposure of hazardous materials from SBRI, to judge the risks associated with the dismantling of EOL ships on open beaches. Our work includes an overview of the industry and its recent growth, compares available ship-breaking methods, provides an inventory of hazardous releases from EOL ships, and reviews their movement into different spheres of the environment. The economic dynamics behind openbeaching, and apportionment of responsibility for hazards related to it, are discussed, in order to generate policy and legal recommendations to mitigate the environmental harm stemming from this industry.