Selective recovery of Cr and Cu in leachate from chromated copper arsenate treated wood using chelating and acidic ion exchange resins

Enhanced synergistic removal of Cu(II) and Cr(VI) with multifunctional biomass hydrogel from strong-acid media

Simultaneous recovery of heavy metal ions (HMIs) such as Cu(II) and Cr(VI) from strong-acid media was a great challenge due to the inhibition of protons. Herein, a novel biomass hydrogel (CMC/PEI-PD) containing various groups (bis-picolylamine, amino, and hydroxyl groups) was newly prepared by a facile two-step process. The static experiments relating pH, kinetics and isothermal co-adsorption confirmed the synergistic effect towards Cu(II) and Cr(VI) consistently. Specifically, the adsorption capacities of Cu(II) and Cr(VI) at pH 2.0 increased by 23.73% and 40.18% in comparison with the single systems. Moreover, coexistence of inorganic anions and cations could further increase the adsorption of Cu(II) and Cr(VI) by 59.90% and 43.39%, respectively. At the same time, the adsorption and desorption ratios for both HMIs remained stable. The superior performance came from the two dominant mechanisms of co-removal. On the one hand, Cu(II) chelated by bis-picolylamine group attracted Cr(VI) in the form of cation bridge, thus promoting Cr(VI) adsorption. On the other hand, the protonated amine group attracted Cr(VI) by electrostatic interaction and weakened the inter-cationic repulsion by electrostatic shielding, thus promoting Cu(II) adsorption. In addition, the dynamic column experiment towards simulated acidic electroplating wastewater involving Cu(II)-Cr(VI)-Ni(II) certified the high efficiency and feasibility of the co-removal. Therefore, CMC/PEI-PD owned great potential in the separation of typical HMIs even directly from strong-acid media.

Bio-Based Hydrogels With Ion Exchange Properties Applied to Remove Cu(II), Cr(VI), and As(V) Ions From Water

Hydrogels with ion exchange properties were synthesized from compounds derived from wood biopolymer hemicellulose and from commercial vinyl monomers to be tested as active materials for the removal of Cu(II), Cr(VI), and As(V) ions. The hemicellulose O-acetyl galactoglucomannan (GGM) was used as the precursor material, and through a transesterification reaction, GGM was converted into a macromonomer GGM–glycidyl methacrylate (GGM-GMA). Subsequently, the GGM-GMA macromonomer, containing more than one methacrylate group, was used as a crosslinking agent in the synthesis of hydrogels through free-radical polymerization reactions in combination with a 2-acrylamido-2-methyl-1-propanesulfonic acid monomer to produce a cation exchange hydrogel. Also, (3-acrylamidopropyl)trimethylammonium chloride monomer was applied together with the GGM-GMA to form hydrogels that can be used as anion exchange hydrogel. The hydrogels were characterized by Fourier transform-infrared (FT-IR), ¹H-NMR spectroscopy, and thermogravimetric analysis (TGA), as well as derivative thermogravimetry (DTG). The microstructure of the hydrogels was characterized by scanning electron microscopy (SEM) analysis with X-ray microanalysis energy-dispersive spectroscopy (EDS). The results obtained regarding the absorption capacity of the Cu(II), Cr(VI), and As(V) ions were studied as a function of the pH value and the initial concentration of the metal ions in the solutions. Absorption was carried out in consecutive batches, and it was found that the poly(GGM-GMA/AMPSH) hydrogel reached an absorption capacity of 90 mg g^–1 for Cu(II). The poly(GGM-GMA/APTACl) hydrogel reached values of 69 and 60 mg g^–1 for Cr(VI) and As(V) oxyanions, respectively. Tests with polymer blends (mixtures of anionic and cationic hydrogels) were also carried out to remove Cu(II), Cr(VI), and As(V) ions from multi-ionic solutions, obtaining satisfactory results.

Adsorption of Pb(II) ions from contaminated water by 1,2,3,4-butanetetracarboxylic acid-modified microcrystalline cellulose: Isotherms, kinetics, and thermodynamic studies

Microcrystalline cellulose (MCC) has been utilized as an adsorbent material for the removal of Pb(II) ions from aqueous solution after treatment with 1,2,3,4-butanetetracarboxylic acid (BTCA) at elevated temperature to obtain MMCC. The resulting adsorbent was characterized for point of zero point charge (pHZPC), estimation of carboxyl content, Fourier transform infrared spectroscopy (FT-IR), scan electron microscopy (SEM), and textural properties, including surface area, and subsequently utilized for the removal of Pb(II) ions from aqueous solution. The adsorption process was probed by investigating the effect of adsorbent dose, pH of solution, temperature, agitation time, and Pb(II) ion concentration. The results showed successful functionalization of MCC using BTCA, significantly improved the binding properties of the adsorbent towards Pb(II) ions. Isothermal adsorption data was analyzed using Langmuir, Freundlich and Temkin models, evaluated via nonlinear regression analysis. The maximum adsorption capacity was found to be 1155 mg/g (at pH 5 and 30 °C) from Langmuir theory, and appears independent of surface area. The Freundlich model was found to provide the best fit and the constant n was determined to be 2.69, indicating that adsorption of Pb(II) ions onto MMCC is favorable. Kinetic modelling showed good agreement for the pseudo-second order kinetic model, supporting the theory that chemisorption is involved in the adsorption process, which is promoted by a high density of active sites. Thermodynamic analysis showed that the adsorption of Pb(II) ions onto MMCC was endothermic and nonspontaneous; hence, MMCC offers an effective method of Pb(II) ion removal from aqueous solutions, with potential for water remediation processes.

Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment

Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.

Response surface methodology investigation into optimization of the removal condition and mechanism of Cr(Ⅵ) by Na2SO3/CaO

The removal of Cr(Ⅵ) by chemical reduction-precipitation is widely applied in wastewater treatment plants. Nevertheless, the formation of Cr(OH)₃ with gel properties has weak settlement performance, making it necessary to add a coagulant aid to reduce the settling time and improve the settling effect. In this investigation, a high concentration of Cr(Ⅵ) was removed using Na₂SO₃ as a reducing agent and CaO as a coagulant. An improved reduction and precipitation experiment was modeled by applying a three-factor central composite experimental design (CCD). To reveal as many mechanisms as possible for Cr_T removal, other verification experiments were performed. The Cr_T removal efficiency decreased, which can be explained by the following three reasons: dissolution of Cr(Ⅲ), competition for adsorption between Ca²⁺ and Cr(Ⅲ) at different coagulation times, and formation of a solubility complex with Cr(Ⅲ) due to the surplus SO₃^2- in solution. The increasing Cr_T removal efficiency can be explained by the following two reasons: dissolved Ca²⁺ from CaO can neutralize CrO₂^- that is produced by the dissolution of Cr(OH)₃ in alkaline solution and can broaden the optimal final pH range of coagulation. Ca²⁺ could also strengthen the Cr_T removal through adsorption bridging and co-precipitation with CaO as the core of flocs.

Treatment technologies used for the removal of As, Cr, Cu, PCP and/or PCDD/F from contaminated soil: A review

The contamination of soils by metals such as arsenic, chromium, copper and organic compounds such as pentachlorophenol (PCP) and dioxins and furans (PCDD/F) is a major problem in industrialized countries. Excavation followed by disposal in an appropriate landfilling is usually used site to manage these contaminated soils. Many researches have been conducted to develop physical, biological, thermal and chemical methods to allow the rehabilitation of contaminated sites. Thermal treatments including thermal desorption seemed to be the most appropriate methods, allowing the removal of more than 99.99% of organic contaminants but, they are ineffective for inorganic compounds. Biological treatments have been developed to remove inorganic and hydrophobic organic contaminants but their applications are limited to soils contaminated by easily biodegradable organic compounds. Among the physical technologies available, attrition is the most commonly used technique for the rehabilitation of soils contaminated by both organic and inorganic contaminants. Chemical processes using acids, bases, redox agents and surfactants seemed to be an interesting option to simultaneously extract organic and inorganic contaminants from soils. This paper will provide an overview of the recent developments in the field of decontamination technologies applicable for the removal of As, Cr, Cu, PCP and/or PCDD/F from contaminated soils.

Visible-light-driven photocatalytic reduction of Cr(vi) on magnetite/carboxylate-rich carbon sheets

The Fe(ii)/Fe(iii) photoredox cycle of Fe₃O₄/carboxylate-rich carbon sheets exhibits excellent visible-light-driven photoreduction activities of Cr(vi).

Decontamination of CCA-treated eucalyptus wood waste by acid leaching

Preservatives such as chromated copper arsenate (CCA) are used to increase the resistance of wood to deterioration. The components of CCA are highly toxic, resulting in growing concern over the disposal of the waste generated. The aim of this study was to investigate the removal of Cu, Cr and As present in CCA-treated eucalyptus wood from utility poles removed from service in southern Brazil, in order to render them non-hazardous waste. The removal was carried out by acid leaching in bench-scale and applying optimal extractor concentration, total solid content, reactor volume, temperature and reaction time obtained by factorial experiments. The best working conditions were achieved using three extraction steps with 0.1 mol L(-1) H2SO4 at 75°C for 2h each (total solid content of 15%), and 3 additional 1h-long washing steps using water at ambient temperature. Under these conditions, removal of 97%, 85% and 98% were obtained for Cu, Cr and As, respectively, rendering the decontaminated wood non-hazardous waste. The wastewater produced by extraction showed acid pH, high organic loading as well as high concentrations of the elements, needing prior treatment to be discarded. However, rinsing water can be recycled in the extraction process without compromising its efficiency. The acid extraction is a promising alternative for CCA removal from eucalyptus wood waste in industrial scale.

Optimization of bioleaching conditions for metal removal from CCA-treated wood by using an unknown Polyporales sp. KUC8959

The purpose of this study was to investigate the effect of extraction conditions (i.e., culture filtrate concentration, extraction temperature, and extraction time) on the removal of metals from chromated copper arsenate (CCA)-treated wood particles by using an unknown Polyporales sp. KUC8959. As the first research, a 20-run central composite design using response surface methodology was applied to optimize the system and construct the models, which predicted metal removal by bioleaching. The coefficients of determination of fitted models were 0.874-0.989, which indicated that the models can predict the metal removal yield accurately under various conditions. The Cu removal model suggested that the following conditions, culture filtrate concentration of 45.8%, extraction temperature of 34.2 °C, and extraction time of 20.6 h, were required for maximal removal of Cu (82.1%). The model predicted that extraction conditions of increased severity would result in complete removal of Cr and As from CCA-treated wood particles. In order to confirm actual metals removal efficiency, metals extraction was subsequently conducted under optimal bioleaching condition evaluated in this study. By applying the model, we demonstrated 83.9% Cu, 96.0% Cr, and 99.3% As removal from treated wood particles.

Polyacrylonitrile/polypyrrole core/shell nanofiber mat for the removal of hexavalent chromium from aqueous solution

Polyacrylonitrile/polypyrrole (PAN/PPy) core-shell structure nanofibers were prepared via electrospinning followed by in situ polymerization of pyrrole monomer for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. Attenuated total reflections Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) results confirmed the presence of the polypyrrole (PPy) layer on the surface of PAN nanofibers. The morphology and structure of the core-shell PAN/PPy nanofibers were studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM), and the core-shell structure can be clearly proved from the SEM and TEM images. Adsorption results indicated that the adsorption capacity increased with the initial solution pH decreased. The adsorption equilibrium reached within 30 and 90 min as the initial solution concentration increased from 100 to 200mg/L, and the process can be described using the pseudo-second-order model. Isotherm data fitted well to the Langmuir isotherm model. Thermodynamic study revealed that the adsorption process is endothermic and spontaneous in nature. Desorption results showed that the adsorption capacity can remain up to 80% after 5 times usage. The adsorption mechanism was also studied by XPS.

Counter-current acid leaching process for copper azole treated wood waste

This study explores the performance of a counter-current leaching process (CCLP) for copper extraction from copper azole treated wood waste for recycling of wood and copper. The leaching process uses three acid leaching steps with 0.1 M H2SO4 at 75degrees C and 15% slurry density followed by three rinses with water. Copper is recovered from the leachate using electrodeposition at 5 amperes (A) for 75 min. Ten counter-current remediation cycles were completed achieving > or = 94% copper extraction from the wood during the 10 cycles; 80-90% of the copper was recovered from the extract solution by electrodeposition. The counter-current leaching process reduced acid consumption by 86% and effluent discharge volume was 12 times lower compared with the same process without use of counter-current leaching. However, the reuse of leachates from one leaching step to another released dissolved organic carbon and caused its build-up in the early cycles.

Sequential electrokinetic treatment and oxalic acid extraction for the removal of Cu, Cr and As from wood

Removal of Cu, Cr and As from utility poles treated with chromated copper arsenate (CCA) was investigated using different one- to three-step combinations of oxalic acid extraction and electrokinetic treatment. The experiments were carried out at room temperature, using 0.8% oxalic acid and 30 V (200 V/m) of direct current (DC) or alternating current in combination (DC/AC). Six-hour extraction removed only 15%, 11% and 28% and 7-day electrokinetic treatment 57%, 0% and 17% of Cu, Cr and As from wood chips, respectively. The best combination for all the metals was a three-step process consisting of pre-extraction, electrokinetics and post-extraction steps, yielding removals of 67% for Cu, 64% for Cr and 81% for As. Oxalic acid extraction prior to electrokinetic treatment was deleterious to further removal of Cu, but it was necessary for Cr and As removal. Chemical equilibrium modelling was used to explain the differences in the behaviour of Cu, Cr and As. Due to the dissimilar nature of these metals, it appeared that even more process sequences and/or stricter control of the process conditions would be needed to obtain the >99% removals required for safe recycling of the purified wood material.