Removal of copper,chromium, and arsenic from CCA-C treated wood by EDTA extraction

Ethylenediaminetetracetic acid (EDTA) is one of the most common chelators used to bind the metal ions in extremely stable complexes in heavy metal contaminated soils and thus to remediate such substrates. EDTA forms water soluble complexes with many metal ions and it is used to release the various metals. In this study, EDTA extraction of copper, chromium, and arsenic from chromated copper arsenate (CCA-C) treated wood was evaluated using batch leaching experiments. CCA-treated wood samples were extracted with eight different concentrations of EDTA for 4, 8, 18, and 24 h at room temperature. Exposing CCA-treated chips and sawdust to EDTA extraction enhanced removal of CCA components compared with extraction by deionized water. Grinding CCA-treated wood chips into 40-mesh sawdust provided greater access to and removal of CCA components. Extraction with 1% EDTA solution for 24 h removed 60% copper, 13% chromium, and 25% arsenic from treated chips. EDTA extraction of treated sawdust samples resulted in 93% copper, 36% chromium, and 38% arsenic removal. CCA leaching from treated wood blocks was also evaluated according to modified AWPA E11-99 standard test method of determining the leachability of wood preservatives. Leaching of CCA components from treated wood blocks with 1% EDTA solution for 14 days caused more copper leaching compared to leaching with deionized water. Leaching with 1% EDTA for 14 days removed 53% copper from the blocks whereas 14% copper was leached from the blocks with deionized water. The results suggest that EDTA extraction removes significant quantities of copper from CCA-treated wood. Thus, EDTA could be important in the remediation of wood waste treated with the newest formulations of organometalic copper compounds and other water-borne wood preservatives containing copper.     

Designing a purification process for chromium-, copper- and arsenic-contaminated wood

The disposal of chromated copper arsenate (CCA)-treated wood is becoming a serious problem in many countries due to increasing levels of contamination by the hazardous elements, chromium, copper and arsenic. The present experiment was conducted as a preliminary step toward one-step solvent extraction of CCA-treated wood. Because chromium, copper and arsenic have different chemical characteristics, it is best to consider them separately prior to designing a one-step extraction process. As a basis, various two-step extraction processes were first designed and tested experimentally to determine feasibility. Among these combinations, the treatment combining oxalic acid as the 1st step and a sodium oxalate solution under acidic conditions (pH 3.2) as the 2nd step was found to be an effective way of extracting CCA elements from treated wood. Extraction efficiency reached 100% for arsenic and chromium and 95.8% for copper after a 3-h sodium oxalate treatment, following a 1-h pre-extraction process with oxalic acid. On the other hand, the same combination under alkaline conditions (pH 11.2) during the 2nd step was ineffective for copper removal, indicating that pH plays an important role in complexation with sodium oxalate solution. The present results suggest that the extraction of CCA elements using a combination of oxalic acid and acidic sodium oxalate solution is a promising basis for application to a one-step extraction method.     

Rapid-extraction oxidation process to recover and reuse copper chromium and arsenic from industrial wood preservative sludge

Chromated copper arsenate (CCA) wood preservative can form insoluble sludges when the hexavalent chromium component is reduced by wood extractives, wood particles and preservative additives in the solution. This sludge accumulates in treating solution work tanks, sumps and in-line filters and must be disposed of as hazardous wastes by waste disposal companies at high costs. A number of commercial sludges were investigated and found to contain 18-94% copper, chromium and arsenic as oxides combined with sand, oil, wood particles, additives and wood extractives. We have developed a multi-stage recycling process whereby approximately 97% of the CCA components are recovered from the sludge. It involves extraction with sodium hypochlorite to remove and oxidize chromium (more than 90%) and extract most of the arsenic (approx. 80%) followed by extraction of the copper and remaining arsenic and chromium with phosphoric acid. The phosphoric acid extract contains some trivalent chromium, which is subsequently oxidized by sodium hypochlorite. The combined oxidized extract containing CrVI, CuII and AsV was compatible with CCA treating solutions and could be re-used commercially for treating wood without having a significant effect on the preservative fixation rate or the leach resistance of the treated wood. A cost analysis showed that the economic savings from recovery of CCA chemicals and reduced landfill costs exceeded the variable costs for materials and energy for the process by as much as Can $966 per tonne of sludge if sodium sulfite can be acquired in bulk quantities for the process.     

Method to recover and reuse chromated copper arsenate wood preservative from spent treated wood

The volume of chromated copper arsenate (CCA) treated wood products coming out of service is expected to increase dramatically during the next decade. There is a need for an alternative waste management approach to landfilling. This paper investigates the variables affecting extraction of CCA components from wood particles and the potential to oxidize and reuse the recovered chemicals. Most of the CCA components could be extracted by 10% H2O2 at 50 degrees C in 6 h with an average extraction efficiency of 95% for Cr, 94% for Cu and 98% for As. The extract containing Cr(III), Cu(II) and As(V) could be oxidized in several stages by aqueous 2.5% w/w H2O2 in less than 2 h to a condition where it was compatible with CCA treating solutions and could be reused for treating new wood. When the recovered extract was mixed with fresh CCA solution in different ratios, the mixed CCA-C solutions had similar solution stability as freshly prepared CCA-C solution and treated wood had similar leaching properties as wood treated with fresh solution.     

Evaluation of XRF and LIBS technologies for on-line sorting of CCA-treated wood waste

Contamination of wood waste with chromated copper arsenate greatly limits recycling opportunities for the wood waste as a whole. Separation of CCA-treated wood from other wood types is one means by which such contamination can be removed. The purpose of the current study was to evaluate two detector technologies for sorting CCA-treated wood from other wood types. The detector technologies evaluated included X-ray fluorescence spectroscopy (XRF) and laser induced breakdown spectroscopy (LIBS). The XRF detector system utilized in this study was capable of rapidly detecting the presence of CCA in painted wood, wet wood, heartwood, sapwood, and at portions of the wood containing knots. Furthermore, the XRF system was capable of distinguishing between CCA-treated wood and wood treated with alternative wood treatment preservatives, but was limited by the fact that it was not designed for on-line operation so tests were conducted in a batch mode on a conveyor. The analysis time used in this study (3 s) can be decreased significantly for an XRF system designed specifically for on-line operation. The LIBS system developed for this study was found to effectively identify CCA-treated wood for pieces ranging in thickness from 1 to 8 cm. High sorting efficiencies were noted when 10 laser shots were taken on a piece of wood. Furthermore, the LIBS system was found to be effective for identifying wood that has been coated with stains and paints in addition to identifying wood that has been CCA treated. The major drawback with the LIBS system developed in this study was the limited laser pulse energy. With an increase in laser pulse energy it is anticipated that the working focal length of the LIBS system can be increased to enable the monitoring of wood samples of more variable thicknesses. Limitations associated with analysis of very rotted pieces of wood and wet wood can also be overcome by using a higher pulse energy laser. Overall, both technologies show incredible promise for sorting CCA-treated wood from other wood types. The next recommended step would be to run an improved full-scale operation at one facility to document sorting efficiencies and fine-tune the improvements proposed in the current study. Such a study could potentially open-the-door for more widespread sorting of wood waste.     

CCA-treated wood disposed in landfills and life-cycle trade-offs with waste-to-energy and MSW landfill disposal

Chromated copper arsenate (CCA)-treated wood is a preservative treated wood construction product that grew in use in the 1970s for both residential and industrial applications. Although some countries have banned the use of the product for some applications, others have not, and the product continues to enter the waste stream from construction, demolition and remodeling projects. CCA-treated wood as a solid waste is managed in various ways throughout the world. In the US, CCA-treated wood is disposed primarily within landfills; however some of the wood is combusted in waste-to-energy (WTE) facilities. In other countries, the predominant disposal option for wood, sometimes including CCA-treated wood, is combustion for the production of energy. This paper presents an estimate of the quantity of CCA-treated wood entering the disposal stream in the US, as well as an examination of the trade-offs between landfilling and WTE combustion of CCA-treated wood through a life-cycle assessment and decision support tool (MSW DST). Based upon production statistics, the estimated life span and the phaseout of CCA-treated wood, recent disposal projections estimate the peak US disposal rate to occur in 2008, at 9.7 million m(3). CCA-treated wood, when disposed with construction and demolition (C&D) debris and municipal solid waste (MSW), has been found to increase arsenic and chromium concentrations in leachate. For this reason, and because MSW landfills are lined, MSW landfills have been recommended as a preferred disposal option over unlined C&D debris landfills. Between landfilling and WTE for the same mass of CCA-treated wood, WTE is more expensive (nearly twice the cost), but when operated in accordance with US Environmental Protection Agency (US EPA) regulations, it produces energy and does not emit fossil carbon emissions. If the wood is managed via WTE, less landfill area is required, which could be an influential trade-off in some countries. Although metals are concentrated in the ash in the WTE scenario, the MSW landfill scenario releases a greater amount of arsenic from leachate in a more dilute form. The WTE scenario releases more chromium from the ash on an annual basis. The WTE facility and subsequent ash disposal greatly concentrates the chromium, often oxidizing it to the more toxic and mobile Cr(VI) form. Elevated arsenic and chromium concentrations in the ash leachate may increase leachate management costs.     

Improving the two-step remediation process for CCA-treated wood: Part I. Evaluating oxalic acid extraction

In this study, three possible improvements to a remediation process for chromated-copper-arsenate- (CCA) treated wood were evaluated. The process involves two steps: oxalic acid extraction of wood fiber followed by bacterial culture with Bacillus licheniformis CC01. The three potential improvements to the oxalic acid extraction step were (1) reusing oxalic acid for multiple extractions, (2) varying the ratio of oxalic acid to wood, and (3) using a noncommercial source of oxalic acid such as Aspergillus niger, which produces oxalic acid as a metabolic byproduct. Reusing oxalic acid for multiple extractions removed significant amounts of copper, chromium, and arsenic. Increasing the ratio of wood to acid caused a steady decline in metal removal. Aspergillus niger removed moderate amounts of copper, chromium, and arsenic from CCA-treated wood. Although A. niger was effective, culture medium costs are likely to offset any benefits. Repeated extraction with commercial oxalic acid appears to be the most cost-effective method tested for the two-step process.     

THE POTENTIAL FOR RE-USE OF PRESERVATIVE-TREATED UTILITY POLES REMOVED FROM SERVICE

This study investigates the feasibility of re-using or recycling utility poles or parts of poles for solid wood products. Four hundred and fifty-six poles or pole sections, removed from service in Ontario and Quebec, Canada, were characterized by age, wood species, preservative type, residual preservative, dimensions and condition. Based on this characterization, the potential for re-use as round poles or posts, sawn posts, timber, lumber and cedar roof shingles was evaluated. About 8% of the poles can be re-used without reprocessing, 15% of the pole volume can be used for cedar shingles, and about 35% of the pole volume can be converted to sawn products based on the selected hierarchy of preferred uses. Most of the poles removed from service had been treated with pentachlorophenol. The average levels of treatment decreased with age of the poles and approached the toxic threshold retentions in 25-year-old (or older) poles. For older poles (>35 years), creosote was the predominant treatment. Creosote levels were about 50% of the assumed levels when fresh treated. Creosote extracted from these poles contained fewer polynuclear aromatic hydrocarbon components than “new” creosote. The poles treated with chromated copper arsenate (CCA) retained high levels of preservative, even after many years in service. Used poles can be sawn into lumber of a good grade (#2 and better) using a small portable bandsaw. Special sawdust handling and disposal provisions must be made if this use is to be adopted. Treated poles with depleted reserves of creosote or pentachlorophenol could be re-treated with CCA or creosote preservatives to acceptable retentions. The quality of re-treatment was as good or better than that observed with new wood, and the re-treatment should ensure several decades of protection for guide-rail posts and other high decay hazard applications.     

Leaching of heavy metals from chromated copper arsenate (CCA) treated wood after disposal

Wood treated by preservatives is commonly found in solid waste. Among the different types of preserved wood, chromated copper arsenate (CCA) treated wood recently has received much attention due to the scale of usage and its significant role in soil and water contamination. As the ash of CCA treated wood would be hazardous if the wood were to be incinerated, this is not a good alternative, and the best available disposal method is thus landfilling in the US, Canada and Australia. Leaching of the metals from preserved wood that is disposed in unlined landfills for construction debris pollutes the soil and water environments. Several factors affecting leaching of the metals from wood, including pH of the leachant, temperature, the duration of leaching and the type of leachant, were investigated. These factors affect each of the metals, chromium, copper and arsenic, differently. A comparison of these effects on each metal was performed. The results of the experiments showed that the pH of the leachants has a significant effect on the leaching process, and sulfuric acid (pH 3) is the most effective leachant compared to nitric and acetic acid (pH 3-4-5). The amounts of leached chromium, copper and arsenic by sulfuric acid (pH 3) during 15 days were, respectively, 0.2, 0.14 and 0.15 mg more than leachates by nitric acid (pH 5) on the basis of 1g of wood (initial contents of 1.03 mg, 0.42 g and 0.8 mg per g of wood). Most of the leaching occurs in the first 5 days, and the rate of leaching decreases significantly after 5 days. Increasing temperature increases the amount of leached metals, and arsenic is the least resistant metal to the leaching when the temperature increases. Increasing the temperature from 15 degrees C to 35 degrees C during 15 days increases the amount of leached chromium, copper and arsenic by acetic acid at pH 5 by about 0.1, 0.4 and 1.2mg per g of wood, respectively.     

Evaluation of commercial landscaping mulch for possible contamination from CCA

Wood treated with chromated copper arsenate (CCA) is found in construction and demolition (C&D) debris, and a common use for wood recycled from C&D debris is the production of mulch. Given the high metals concentrations in CCA-treated wood, a small fraction of CCA-treated wood can increase the metal concentrations in the mulch above regulatory thresholds. The objective of this study was to determine the extent of contamination of CCA-treated wood in consumer landscaping mulch and to determine whether visual methods or rapid X-ray fluorescence (XRF) technology can be used to identify suspect mulch. Samples were collected throughout the State of Florida (USA) and evaluated both visually and chemically. Visual analysis focused on documenting wood-chip size distribution, whether the samples were artificially colored, and whether they contained plywood chips which is an indication that the sample was, in part, made from recycled C&D wood. Chemical analysis included measurements of total recoverable metals, leachable metals as per the standardized synthetic precipitation leaching procedure (SPLP), and XRF analysis. Visual identification methods, such as colorant addition or presence of plywood, were found effective to preliminarily screen suspect mulch. XRF analysis was found to be effective for identifying mulch containing higher than 75 mg/kg arsenic. For mulch samples that were not colored and did not contain evidence of C&D wood, none exceeded leachable metal concentrations of 50 microg/L and only 3% exceeded 10 mg/kg for recoverable metals. The majority of the colored mulch made from recycled C&D wood contained from 1% to 5% CCA-treated wood (15% maximum fraction) resulting in leachable metals in excess of 50 microg/L and total recoverable metals in excess of 10 mg/kg. The maximum arsenic concentration measured in the mulch samples evaluated was 230 mg/kg, which was above the Florida residential direct exposure regulatory guideline of 2.1 mg/kg.     

Improving the two-step remediation process for CCA-treated wood: Part II. Evaluating bacterial nutrient sources

Remediation processes for recovery and reuse of chromated-copper-arsenate- (CCA) treated wood are not gaining wide acceptance because they are more expensive than landfill disposal. One reason is the high cost of the nutrient medium used to culture the metal-tolerant bacterium, Bacillus licheniformis, which removes 70-100% of the copper, chromium, and arsenic from CCA-treated southern yellow pine (CCA-SYP) in a two-step process involving oxalic acid extraction and bacterial culture. To reduce this cost, the nutrient concentration in the culture medium and the ratio of wood to nutrient medium were optimized. Maximum metal removal occurred when B. licheniformis was cultured in 1.0% nutrient medium and at a wood to nutrient medium ratio of 1:10. Also, malted barley, an abundant by-product of brewing, was evaluated as an alternative nutrient medium. Tests were done to determine absorption of metals by barley, and the results indicate that the barley acted as a biosorbent, removing heavy metals from the liquid culture after their release from CCA to SYP. For comparison, tests were also performed with no nutrient medium. Following bacterial remediation, 17% copper and 15% arsenic were removed from an aqueous slurry of CCA-SYP (no medium). When oxalic acid extraction preceded the aqueous bacterial culture, 21% copper, 54% chromium, and 63% arsenic were removed. The two-step process (oxalic acid extraction and bacterial culture with nutrient medium) appears to be an effective, yet costly, way to remove metals.     

Evaluation of methods for sorting CCA-treated wood

Construction and demolition (C&D) wood frequently contains treated wood including wood treated with chromated copper arsenate (CCA). Many recycling options for such wood require that the product be essentially free of preservative chemicals. The objectives of this study were to document the characteristics of the wood waste stream and to evaluate the effectiveness of sorting methods for identifying treated wood. Sorting methods evaluated included visual sorting and visual sorting augmented with the use of PAN indicator stain and/or hand-held X-ray fluorescence (XRF) units. Experiments were conducted on two types of construction and demolition (C&D) wood: source separated loads containing only C&D wood and wood hand-picked from commingled loads of general C&D waste. Results showed that 77% of the treated wood was CCA-treated. For uncontaminated piles (<1% treated wood) of source separated C&D wood, visual sorting was found to effectively remove the small amounts of treated wood present. For piles of source separated wood that were contaminated (approximately 50% treated wood), visual sorts were not accurate and benefited from augmented sorting using PAN indicator stain. The handheld XRF devices were found to be effective for sorting commingled C&D wood, as PAN indicator stain was not as effective due to the excessive amount of surface dirt associated with commingled wood waste. Visual sorting of source separated wood was estimated to cost between US$21 to US$96 per metric ton. These costs depended upon the amount of treated wood and whether or not augmentation with PAN indicator was necessary. Visual sorting augmented with hand-held XRF units was estimated at US$113 per metric ton. The bulk of these costs were associated with labor. Future efforts should focus on reducing labor costs by mounting automated XRF units on conveyor systems.     

Removal of copper,chromium and arsenic from preservative-treated wood by chemical extraction-fungal bioleaching

Large volumes of preservative-treated wood containing toxic Cr, Cu and As salts are decommissioned worldwide. This study investigated the effectiveness of solid-state fermentation with copper-tolerant brown-rot fungi for the remediation of wood treated with chromated copper arsenate (CCA) and acid copper chromate (ACC) formulations. Treatment of CCA- and ACC-wood with the most effective strain, Antrodia vaillantii FRLP-14G, attained extensive leaching of As and/or Cr, but Cu elimination was poor (<18%). Additional research showed that a variety of organic acids, including citrate, are effective Cu extractants. Based on these findings, a process combining chemical extraction and subsequent fungal treatment was developed that proved highly effective in removing inorganic pollutants from CCA-wood. Extraction of CCA-wood with citric acid (30 mM, pH 3.10) followed by a 28-day solid-state fermentation period removed 87% Cu, 80% Cr, and 100% As. These results indicate the potential of the two-stage process for the remediation of preservative-treated wood.     

Evaluation of the potential of applying composting/bioremediation techniques to wastes generated within the construction industry

The objective of the present study was to evaluate the viability of reducing landfill requirements to satisfy EC Landfill Directive requirements by applying composting/bioremediation techniques to the construction and demolition (C&D) industry waste stream at laboratory scale. The experimental study was carried out in nine test rigs to examine different wood mixtures; untreated timber, creosote treated timber and chromated copper arsenate (CCA) treated timber. Several experimental variables affecting the process were characterised and optimised. These include the best nitrogen additive and optimum moisture content required for composting. Poultry manure was found to be the best nitrogen additive. The optimum moisture content was decreased after the addition of poultry manure. The composting/bioremediation process was evaluated through monitoring the microbial activity, carbon dioxide emissions and toxicity examination of the composted product. A typical temperature profile suggested that untreated and CCA treated mix could be classified as hot composting whereas creosote treated mix could be classified as cold composting. The paper reports on the results obtained during this investigation.     

Exergy analysis of the Chartherm process for energy valorization and material recuperation of chromated copper arsenate (CCA) treated wood waste

The Chartherm process (Thermya, Bordeaux, France) is a thermochemical conversion process to treat chromated copper arsenate (CCA) impregnated wood waste. The process aims at maximum energy valorization and material recuperation by combining the principles of low-temperature slow pyrolysis and distillation in a smart way. The main objective of the exergy analysis presented in this paper is to find the critical points in the Chartherm process where it is necessary to apply some measures in order to reduce exergy consumption and to make energy use more economic and efficient. It is found that the process efficiency can be increased with 2.3-4.2% by using the heat lost by the reactor, implementing a combined heat and power (CHP) system, or recuperating the waste heat from the exhaust gases to preheat the product gas. Furthermore, a comparison between the exergetic performances of a ‘chartherisation’ reactor and an idealized gasification reactor shows that both reactors destroy about the same amount of exergy (i.e. 3500 kW kg_wood⁻¹) during thermochemical conversion of CCA-treated wood. However, the Chartherm process possesses additional capabilities with respect to arsenic and tar treatment, as well as the extra benefit of recuperating materials.     

Online sorting of recovered wood waste by automated XRF-technology. Part I: detection of preservative-treated wood waste

Waste wood is frequently contaminated with wood treatment preservatives including chromated copper arsenate (CCA) and alkaline copper quat (ACQ), both of which contain metals which contaminate recycled wood products. The objective of this research was to propose a design for online automated identification of As-based and Cu-based treated wood within the recovered wood waste stream utilizing an X-ray fluorescence (XRF) system, and to evaluate the detection parameters of such system. A full-scale detection unit was used for experimentation. Two main parameters (operational threshold (OT) and measurement time) were evaluated to optimize detection efficiencies. OTs of targeted metals, As and Cu, in wood were reduced to 0.02 and 0.05, respectively. The optimum minimum measurement time of 500 ms resulted in 98%, 91%, and 97% diversion of the As, Cu and Cr mass originally contained in wood, respectively. Comparisons with other detection methods show that XRF technology can potentially fulfill the need for cost-effective processing at large facilities (>30 tons per day) which require the removal of As-based preservatives from their wood waste stream.     

Thermal and hydrometallurgical recovery methods of heavy metals from municipal solid waste fly ash

Heavy metals in fly ash from municipal solid waste incinerators are present in high concentrations. Therefore fly ash must be treated as a hazardous material. On the other hand, it may be a potential source of heavy metals. Zinc, lead, cadmium, and copper can be relatively easily removed during the thermal treatment of fly ash, e.g. in the form of chlorides. In return, wet extraction methods could provide promising results for these elements including chromium and nickel. The aim of this study was to investigate and compare thermal and hydrometallurgical treatment of municipal solid waste fly ash. Thermal treatment of fly ash was performed in a rotary reactor at temperatures between 950 and 1050 °C and in a muffle oven at temperatures from 500 to 1200 °C. The removal more than 90% was reached by easy volatile heavy metals such as cadmium and lead and also by copper, however at higher temperature in the muffle oven. The alkaline (sodium hydroxide) and acid (sulphuric acid) leaching of the fly ash was carried out while the influence of temperature, time, concentration, and liquid/solid ratio were investigated. The combination of alkaline-acidic leaching enhanced the removal of, namely, zinc, chromium and nickel.     

Recycling and reuse of waste from electricity distribution networks as reinforcement agents in polymeric composites

Of the waste generated from electricity distribution networks, wooden posts treated with chromated copper arsenate (CCA) and ceramic insulators make up the majority of the materials for which no effective recycling scheme has been developed. This study aims to recycle and reuse this waste as reinforcement elements in polymer composites and hybrid composites, promoting an ecologically and economically viable alternative for the disposal of this waste. The CCA wooden posts were cut, crushed and recycled via acid leaching using 0.2 and 0.4 N H₂SO₄ in triplicate at 70 °C and then washed and dried. The ceramic insulators were fragmented in a hydraulic press and separated by particle size using a vibrating sieve. The composites were mixed in a twin-screw extruder and injected into the test specimens, which were subjected to physical, mechanical, thermal and morphological characterization. The results indicate that the acid treatment most effective for removing heavy metals in the wood utilizes 0.4 N H₂SO₄. However, the composites made from wood treated with 0.2 N H₂SO₄ exhibited the highest mechanical properties of the composites, whereas the use of a ceramic insulator produces composites with better thermal stability and impact strength. This study is part of the research and development project of ANEEL (Agência Nacional de Energia Elétrica) and funded by CPFL (Companhia Paulista de Força e Luz).     

Potential Remobilization of Toxic Anions during Reduction of Arsenated and Chromated Schwertmannite by the Dissimilatory Fe(III)-Reducing Bacterium Acidiphilium cryptum JF-5

Schwertmannite, an iron(III)-oxyhydroxysulfate formed in acidic mining-impacted stream or lake waters often contaminated with toxic elements like arsenate or chromate, is able to incorporate high amounts of these oxyanions. Detoxification of the water might be achieved if precipitated arsenated or chromated schwertmannite is fixed in the sediment. However, under reduced conditions, reductive dissolution of iron oxides mediated by the activity of Fe(III)-reducing bacteria might mobilize arsenate and chromate again. In this study, the reduction of synthesized arsenated or chromated schwertmannite by the acidophilic Fe(III)-reducer Acidiphilium cryptum JF-5, isolated from an acidic mining-impacted sediment, was investigated. In TSB medium at pH 2.7 with glucose as electron donor, A. cryptum JF-5 reduced about 10% of the total Fe(III) present in pure synthetic schwertmannite but only 5% of Fe(III) present in arsenated schwertmannite. In contrast to sulfate that was released during the reductive dissolution of pure schwertmannite, arsenate was not released during the reduction of arsenated schwertmannite probably due to the high surface complexation constant of arsenate and Fe(III). In medium containing chromated schwertmannite, no Fe(II) was formed, and no glucose was consumed indicating that chromate might have been toxic to cells of A. cryptum JF-5. Both As(V) or Cr(VI) could not be utilized as electron acceptor by A. cryptum JF-5. A comparison between autoclaved (121 °C for 20 min) and non-autoclaved schwertmannite samples demonstrated that nearly 100%of the bound sulfate was released during heating, and FTIR spectra indicated a transformation of schwertmannite to goethite. This structural change was not observed with autoclaved arsenated or chromated schwertmannite. These results suggest that the mobility of arsenate and chromate is not enhanced by the activity of acidophilic Fe(III)-reducing bacteria in mining-impacted sediments. In contrast, the presence of bound arsenate and chromate seemed to stabilize schwertmannite against reductive dissolution and its further transformation to goethite that is an ongoing process in those sediments.     

The Chartherm process,what’s in the name?

Earlier research has identified the Chartherm process (Thermya, France) as a candidate for the best available technology to treat chromated copper arsenate (CCA) impregnated wood waste. This paper presents the working principle, the characteristics and the current state-of-knowledge related to the process, illustrating clearly the differences with pyrolysis and carbonisation processes. To emphasise the specific nature of the process, it has been given its own name ‘chartherisation’. The avoidance of tar and dioxin release, the role of the solid matrix in the metal behaviour and the separation process are described. Furthermore, the possible benefits of working at elevated pressure are discussed, based on the experience with charcoal production from coal and biomass. This paper shows that more fundamental research is needed to understand and model all mechanisms contributing to the characteristic nature of chartherisation, in order to control the dynamic behaviour and tune the operating conditions in the reactor on the quality of the products requested.