Leaching Retention of CCA Metals from High- Temperature Reaction with Alkaline Earth and Iron Based Sorbents (original) (raw)
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Chromated copper arsenate (CCA) treated wood is the popular treated wood found in the wood waste disposal sector. Incineration has been a key disposal pathway for CCA-treated wood waste; however, the potential for emissions of toxic metals from combustion, and their accumulation and subsequent leaching from ash has raised public concerns. Earlier studies by our group focused on evaluating combinations of CCA chemical with sorbents for their ability to minimize leaching of ash. The objective of this study was to evaluate the ability of sorbents to minimize the leaching of CCA-treated wood and to compare the results to evaluate the influence of the wood matrix on the effectiveness of sorbents to minimize leaching. Experiments were carried out using CCA wood with alkaline earth, alumino-silicate and iron-based sorbents combusted at 700 oC and 1100 oC. A portion of the residual was leached using the toxicity characteristic leaching procedure (TCLP). Alkaline earth sorbents (cement and Mg(OH)2) successfully reduced the leaching of arsenic from the ash to below the TCLP limit. Fe2O3 (iron-based sorbent) and kaolin (alumino-silicate sorbent) were able to achieve low leaching (below TCLP limit) of chromium. For copper, low leaching from baseline CCA wood ash was observed, and alkaline earth sorbents demonstrated the best potential to further lower copper leaching. When the leachate pH was high, low leaching for As and Cu occurred, whereas a lower leachate pH correlated with low chromium leaching. These results are broadly consistent with prior studies using CCA chemicals that showed alkaline-earth sorbents to be effective for As and Cu and Fe2O3 to be effective for Cr. Therefore, a combination of sorbents (like cement and Fe2O3) used at different stages of high-temperature processes involving CCA wood, or burning CCA wood in industrial processes containing these minerals, may effectively control the leaching of CCA metals from CCA-treated wood waste.
Past studies have shown that many alumino-silicate mineral sorbents are effective in controlling heavy metal emission during incineration. The objective of this study was to identify Al-Si based mineral sorbents that can minimize leaching of heavy metals from the incinerator ash of Chromated Copper Arsenate (CCA-) treated wood. Experiments were carried out using CCA metal spikes combined with Al-Si sorbents, heated to 700 oC, 900 oC and 1100 oC for 30 minutes. The residual ash was leached using the toxicity characteristic leaching procedure (TCLP). X-Ray Diffraction (XRD) analysis was conducted to determine the crystalline speciation of the products. Results showed that low leaching was observed for chromium, below the 5 mg/L TC limit, by alumina and silica at all temperatures, and kaolin at higher temperatures (900 oC and 1100 oC). For copper, all sorbents displayed low leaching values (< 51 mg/l) as compared to the baseline. For arsenic, all sorbents exceeded the TC limit. Speciation characterization results revealed the formation of several metal-metal and metal-mineral compounds that might have resulted in different leaching behaviors of each metal-sorbent pair under different combustion conditions. The results suggest that a combination of sorbents at different stages of the combustion process can be effective to control the leaching of CCA metals.
2001
The combustion of recovered wood from construction and demolition waste as biomass fuel is a common practice. When chromated copper arsenate (CCA)-treated wood is present as part of the wood fuel mix, concentrations of arsenic, chromium, and copper become elevated in the ash. The objectives of this study were to estimate the fraction of CCA-treated wood needed to cause the ash to fail regulatory guidelines and to test a series of solvents for the purpose of extracting the metals from the ash. Ash samples were prepared in an industrial furnace using samples of CCA-treated wood, mixtures of CCA-treated wood and untreated wood, and recycled wood waste collected at construction and demolition recycling facilities. Regulatory guidelines were evaluated by measur-ing total metals concentrations (using neutron activation analysis) and by conducting standardized leaching tests (toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leach-ing procedure (SPLP)) on the as...
Characteristics of chromated copper arsenate-treated wood ash
Journal of Hazardous Materials, 2002
The combustion of recovered wood from construction and demolition waste as biomass fuel is a common practice. When chromated copper arsenate (CCA)-treated wood is present as part of the wood fuel mix, concentrations of arsenic, chromium, and copper become elevated in the ash. The objectives of this study were to estimate the fraction of CCA-treated wood needed to cause the ash to fail regulatory guidelines and to test a series of solvents for the purpose of extracting the metals from the ash. Ash samples were prepared in an industrial furnace using samples of CCA-treated wood, mixtures of CCA-treated wood and untreated wood, and recycled wood waste collected at construction and demolition recycling facilities. Regulatory guidelines were evaluated by measuring total metals concentrations (using neutron activation analysis) and by conducting standardized leaching tests (toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP)) on the ash. Ten different solvents, ranging from distilled water to strong acids, were also tested for their ability to extract metals. Results of this study indicate that metal concentrations (chromium plus copper plus arsenic) can be as high as 36% of the ash by weight for treated wood samples containing high retention levels (40 kg/m 3) of CCA. All ash samples from the combustion of 100% CCA-treated wood and mixtures containing 5% CCA-treated wood leached enough arsenic (and sometimes chromium) to be characterized as a hazardous waste under US regulations. Concentrated nitric acid, which was the most effective solvent tested, was capable of removing between 70 and 100% of the copper, between 20 and 60% of the chromium, and 60 and 100% of the arsenic for samples characterized by low retention levels. A particular finding of interest was the efficiency of distilled water and other weak solvents to extract measurable amounts of chromium, especially for ash samples containing low retention levels of CCA.
Leaching of heavy metals from chromated copper arsenate (CCA) treated wood after disposal
Waste Management, 2008
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 1 g 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°C to 35°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 1.2 mg per g of wood, respectively.
Environmental Pollution, 2005
Several alternative methods for the disposal of chromated copper arsenate (CCA) treated wood waste have been studied in the literature, and these methods are reviewed and compared in this paper. Extraction experiments have been carried out on CCA treated wood and evaluated as a method to recover the metal compounds into either fresh wood preservatives or other useful industrial materials. Recycling and recovery processes of the metals in the metallurgical industry have also been studied, but not yet all metal products are transformed to usable forms. A study about biorecycling of CCA treated wood through bioremediation and biodeterioration has been initiated. Numerous studies and experiments have been carried out on burning contaminated wood. Direct electrodialytic removal of the metals from CCA treated wood, as well as electrochemical cleaning processes for ash resulting from combustion of CCA treated wood, are under study. Pyrolysis processes (both slow and flash pyrolysis) have been investigated as a major process for the disposal of cellulosic wastes, also CCA treated wood waste. The authors performed a lot of experimental and theoretical work to get more insight in the metal behaviour during the low-temperature pyrolysis of CCA treated wood waste. Experiments were carried out with CCA treated wood samples, as well as with arsenic model compounds and mixtures of arsenic oxides and reducing agents (glucose or activated carbon). The most important conclusion is that zero arsenic release during pyrolysis of CCA treated wood seems to be impossible since the reduction reaction (As 2 O 5 → As 2 O 3 + O 2 ) can not be avoided in the reducing environment, created by the presence of wood, char and pyrolysis vapours. Once the trivalent arsenic oxide is formed, it is released. This release is driven by a vapour pressure controlled volatilisation process: the higher the temperature, the faster the release. The insights gained through these studies are used to evaluate other thermochemical conversion processes (flash pyrolysis, gasification and combustion) with respect to their applicability to the disposal of CCA treated wood waste. This evaluation is compared with observations and calculations reported by other researchers in the literature. Finally, the most appropriate thermochemical disposal technology is identified.
Energies
Chromated copper arsenate-treated (cca) wood disposal faces environmental restrictions due to its toxicity, heavy metal leaching in storage sites, and greenhouse gas emissions during incineration. Thus, finding new management methods for this contaminated wood at the end of life is crucial. This study evaluated the effect of pyrolysis temperature (300, 400, and 500 °C), particle size, biochar yield, and the behavior of arsenic (As), chromium (Cr), and copper (Cu) during treated-wood pyrolysis. The highest biochar yield was obtained at 300 °C for fine particles. The biochar retention of heavy metals decreased with increasing pyrolysis temperature. At 300 °C, the highest biochar As, Cr, and Cu retentions were 76, 91, and 83%. At 500 °C, biochar only retained 43% of the As. Additionally, heavy metal leaching from the biochar exceeded the Environmental Protection Agency’s (EPA) maximum concentration limit of 5 mg/L. High-density polyethylene encapsulation of contaminated biochar reduced...
Several alternative methods for the disposal of chromated copper arsenate (CCA) treated wood waste have been studied in the literature, and these methods are reviewed and compared in this paper. Extraction experiments have been carried out on CCA treated wood and evaluated as a method to recover the metal compounds into either fresh wood preservatives or other useful industrial materials. Recycling and recovery processes of the metals in the metallurgical industry have also been studied, but not yet all metal products are transformed to usable forms. A study about biorecycling of CCA treated wood through bioremediation and biodeterioration has been initiated. Numerous studies and experiments have been carried out on burning contaminated wood. Direct electrodialytic removal of the metals from CCA treated wood, as well as electrochemical cleaning processes for ash resulting from combustion of CCA treated wood, are under study. Pyrolysis processes (both slow and flash pyrolysis) have been investigated as a major process for the disposal of cellulosic wastes, also CCA treated wood waste. The authors performed a lot of experimental and theoretical work to get more insight in the metal behaviour during the low-temperature pyrolysis of CCA treated wood waste. Experiments were carried out with CCA treated wood samples, as well as with arsenic model compounds and mixtures of arsenic oxides and reducing agents (glucose or activated carbon). The most important conclusion is that zero arsenic release during pyrolysis of CCA treated wood seems to be impossible since the reduction reaction (As 2 O 5 → As 2 O 3 + O 2 ) can not be avoided in the reducing environment, created by the presence of wood, char and pyrolysis vapours. Once the trivalent arsenic oxide is formed, it is released. This release is driven by a vapour pressure controlled volatilisation process: the higher the temperature, the faster the release. The insights gained through these studies are used to evaluate other thermochemical conversion processes (flash pyrolysis, gasification and combustion) with respect to their applicability to the disposal of CCA treated wood waste. This evaluation is compared with observations and calculations reported by other researchers in the literature. Finally, the most appropriate thermochemical disposal technology is identified.
Chromated Copper Arsenate Timber: A Review of Products, Leachate Studies and Recycling
Large volumes of chromated copper arsenate (CCA)-treated wood are disposed of in lined and unlined landfills across the world. Studies regarding the disposal and reuse of CCA-treated timber date back to the 1980s. This paper provides a comprehensive overview of the research undertaken regarding reconstituted chromated copper arsenate-treated timber products, and considers the relevant health issues and disposal techniques, such as incineration and thermochemical conversion, as well as long-term solutions for the managing of chromated copper arsenate-treated-waste wood. The results from reviewing the literature regarding reconstituted timber products consisting of CC-treated timber such as particle board, cement-bonded particle board, flake board, remediated wood composites, wood-plastic composites, and wood-cement composites revealed that products such as particle board, wood-plastic composites and flake board composed of CCA-treated timber show considerable promise. Further research is required to determine the optimum percentage of CCA-treated timber in wood-plastic composites to minimize leaching while attaining suitable physical and mechanical performance, and to evaluate the durability of reconstituted chromated copper arsenate timber products via severe accelerated aging tests. Several CCA-waste wood disposal methods were investigated in the form of extraction and destruction techniques including thermochemical conversion (pyrolysis, gasification), incineration, co-incineration and combustion. Such management techniques demonstrate promising, feasible, future solutions providing the ability to trap arsenic gas, recover metals, and create secondary energy forms. However, more research is required, especially regarding resultant arsenic compounds and their volatile behaviours. Industries that create and sell chromated copper arsenate-treated wood products are encouraged to follow the United States Environmental Protection Agency leachate testing procedures (Methods 1314 and 1315, published in 2013), since these methods are more accurate at evaluating the leaching behaviour during their lifetime, and various disposal scenarios that reflect differing pH values and liquid to solid ratios.