Fractionation of Heavy Metals in Liquefied Chromated Copper Arsenate (CCA)-Treated Wood Sludge Using a Modified BCR-Sequential Extraction Procedure

DrToddShupe Image CCA Agric Fence post
The photo is courtesy of Mike Freeman

Summary of CCA Sequential Extraction

Chromated copper arsenate (CCA)-treated wood was liquefied with polyethylene glycol/glycerin and sulfuric acid. After liquefaction, most CCA metals (98% As, 92% Cr, and 83% Cu) were removed from liquefied CCA-treated wood by precipitation with calcium hydroxide. The original CCA-treated wood and liquefied CCA-treated wood sludge were fractionated by a modified Community Bureau of Reference (BCR) sequential extraction procedure. The purpose of the BCR-sequential extraction used in this study was to examine the availability of CCA metals in treated wood for reuse. Both As and Cr had a slightly higher concentration in the sludge sample than in original CCA-treated wood. The sequential extraction showed that As and Cr were principally existed in an oxidizable fraction (As, 67%; Cr, 88%) in original CCA-treated wood. Only 1% of both As and Cr were extracted by hot nitric acid with the last extraction step. The distribution of As and Cr changed markedly in liquefied CCA-treated wood sludge. The amount of As in the exchangeable/acid extractable fraction increased from 16% to 85% while the amount of Cr increased from 3% to 54%. Only about 3% of As was present in the oxidizable fraction. However, there was still about 34% of Cr in the same fraction. Based on these results from sequential extraction procedures, it can be concluded that the accessibilities of CCA metals increase markedly by the liquefaction–precipitation process.

CCA Removal Methods

For many years, chromated copper arsenate (CCA) was the most commonly used waterborne wood preservative in the world. Despite the decision of the US and Canadian wood preservation industry to voluntarily withdraw the use of CCA-treated wood from residential and consumer uses as of December 31, 2003 (US EPA, 2003), the use of CCA-treated wood for industrial purposes (e.g., utility poles and marine pilings) continues (Song et al., 2006; Block et al., 2007). In addition, with an expected average service life between 20–40 years, the amount of spent CCA-treated wood in the US and Canada will greatly expand from the current 3–4 million m 3/yr  to around 12 million m 3/yr in Canada and the USA within the next 15 years (Cooper, 2003).  Many efforts have been made to develop appropriate alternative technologies for disposal of spent CCA-treated wood other than traditional landfills and incineration, which have raised environmental and human health concerns. A method to remove Cr, Cu, and As from spent CCA-treated wood based on wood liquefaction has been developed by Lin and Hse (2005). They reported that CCA-treated wood can be liquefied under similar liquefaction conditions as non-treated wood and up to 99% of the heavy metals can be removed from CCA-treated wood by adding ferrous salts during the liquefaction stage. In addition, CCA-wood complexes are either released from the decomposed lignin and cellulose or remains as the complexes or chelates with decomposed lignin and cellulose during the liquefaction reaction, which should provide better accessibility for the extractants in the heavy metal removal step.

Although many CCA metal removal methods, such as chemical extraction (Kartal and Clausen, 2001a; Kakitani et al., 2006) and bioremediation (Clausen, 2004b), have been proposed, very few studies have focused on both removal and reuse of CCA metals. It has been generally considered that Cr(VI) is reduced to Cr(III) and which then precipitates with As(V) and Cu(II) in wood components during CCA fixation process. Therefore, it is essential that the recovered CCA metals should be in an appropriate oxidation state which can be reused as a treating solution.

Todd Shupe is the President of DrToddShupe.com and is a well recognized expert on wood-based housing and wood science.  Shupe worked as a  professor and lab director at LSU for 18 years and Quality Manager for Eco Environmental (Louisville, KY) for 2 years. He is active in several ministries including his Christian blog ToddShupe.com. Todd is the Secretary of the Baton Rouge District of United Methodist Men, Database Coordinator for Gulf South Men, and volunteer for the Walk to Emmaus, Grace Camp, Iron Sharpens Iron, Open Air Ministries, HOPE Ministries food pantry. Todd is currently preparing to be a Men’s Ministry Specialist through the General Commission of United Methodist Men.

Rapid Microwave-Assisted Acid Extraction of Metals from Chromated Copper Arsenate Treated Wood

Rapid Microwave used to treat wood
Photo by Karelj

Abstract – Chromated Copper Arsenate Treated Wood

The effects of acid concentration, reaction time, and temperature in a microwave reactor on recovery of CCA-treated wood were evaluated. Extraction of copper, chromium, and arsenic metals from chromated copper arsenate (CCA)-treated southern pine wood samples with three different acids (i.e., acetic acid, oxalic acid, and phosphoric acid) was investigated using in microwave reactor. Oxalic acid was effective in removing 100% of the chromium and arsenic at 160°C and 30 min., and acetic acid could remove 98% of the copper and arsenic at the same conditions. Oxalic acid greatly improved the extraction efficiency of arsenic and chromium when time was prolonged from 10min. to 30min. Acetic acid also showed improved ability to remove arsenic and copper when the reaction temperature was increased from 90°C to 160°C.

Introduction

Preservative-treated wood products are well known to significantly prolong service life, and thereby extend the forest resource and enhance its sustainability. Inevitably, large volumes of preservative-treated wood are decommissioned each year. It is estimated that about 3-4 to 12 million tons of spent preserved wood will be removed from service in the United States and Canada in the next 20 years (Kazi and Cooper, 2006). Disposal of the spent CCA-treated wood has become a major concern because of its residual toxic components, particularly arsenic and chromium. Conventional waste disposal options for spent preserved wood, such as burning and landfilling, are becoming more costly or even impractical because of increasingly strict regulatory requirements (Townsend et al., 2004). The burning of treated wood can be extremely dangerous and even more so when the wood has been treated with CCA. Studies have shown that burning of preservative–treated wood waste emits highly toxic smoke and fumes in the environment (Solo-Gabriele, 2002). In the case of landfills, studies have shown that CCA3 compounds can be gradually leached out (Townsend, 2005; Moghaddam, 2008). Moreover, there is concern regarding landfill capacity. Therefore, there is an urgent need for developing techniques for recycling CCA-treated out of service wood. Several chemical methods have been proposed to extract the metals from CCA-treated wood. Solvent extraction can dissolve the preservatives and partially remove them from the wood. The used of acid extraction to remove CCA components from wood has been extensively studied (Kartal and Clausen, 2001; Son et al., 2003; Clausen, 2003; Clausen, 2004; Gezer, 2006; Kakitani 2006; Kakitani 2007). One of the advantages for acid extraction is based on its potential ability of reversing the CCA fixation process, thereby converting CCA elements into their water-soluble form (Kartal and Clausen, 2001). However, among the disadvantages of this recycling method are the huge amount of chemical solvents used and the long duration of the process. The prevailing treatment times reported ranged from 16 h for sawdust (Clausen and Smith, 1998) to 24 h for chips (Kartal and Clausen, 2001), which are considered to be major factors hindering commercial development. Therefore, to develop an economically viable industrial process, the focus of our study was on treatment time and acid concentration. Thus, the time saving potential of microwave heating led us to its application with acid extraction. The specific objectives of this study were to: (1) develop a new CCA recovery system based on the application of microwave energy, and (2) optimize reaction time, temperature, and acid concentration for the process.

Todd Shupe is the President of DrToddShupe.com and is a well recognized expert on wood-based housing and wood science.  Shupe worked as a  professor and lab director at LSU for 18 years and Quality Manager for Eco Environmental (Louisville, KY) for 2 years. He is active in several ministries including his Christian blog ToddShupe.com. Todd is the Secretary of the Baton Rouge District of United Methodist Men, Database Coordinator for Gulf South Men, and volunteer for the Walk to Emmaus, Grace Camp, Iron Sharpens Iron, Open Air Ministries, HOPE Ministries food pantry. Todd is currently preparing to be a Men’s Ministry Specialist through the General Commission of United Methodist Men.

Pecky Cypress – An American Favorite

Flush-mounted pecky cypress beam accents a salt water fish aquarium and brick wall.

Sometimes Fungi Are Good!

Bald cypress is a deciduous conifer in the family Cupressaceae that grows on saturated and seasonally inundated soils in the lowlands of the Southeastern and Gulf Coastal Plains of the United States.   Like most tree species it has several common names (baldcypress, bald-cypress, cypress, southern-cypress, white cypress, tidewater red-cypress, sinker cypress, Gulf-cypress, red-cypress, or swamp cypress) but only one scientific (Latin) name:  Taxodium distichum.

Cypress wood is without an odor and closely resembles that of other Cupressus species.  It has long been valued for its natural decay resistance.  However, the cypress that is harvested today does not have the same heartwood decay resistance of cypress of the early 1900s.  This fact has been well documented but the reasons for this difference are less clear.  I personally have seen ax cut cypress logs recovered from lakes and rivers.  The lumber cut from these logs is absolutely beautiful.  Bald cypress was designated the official state tree of Louisiana in 1963. Some consider it to be a symbol of the southern swamps of the United States and it is often featured in many swamp paintings and pictures along with Spanish moss.  The early settlers used cypress to produce shakes and shingles for their houses.

Cypress has long been a favorite wood species for furniture and other value-added uses.  It has a unique grain pattern that often includes missing and false rings due to local environmental conditions (i.e., flooding).  A missing ring occurs when no ring is produced in a year and a false ring occurs when multiple rings are produced in one year.  So, be careful when trying to age a cypress log based on visual ring count.  The rings need to be closely examined to distinguish true and false rings.

My favorite feature of cypress is not the false rings but “peck.”  This is a very rare condition and has a high demand and limited supply.  Therefore, if you do find it, be prepared to pay dearly.  I did a quick internet search and found 1×8 tongue and grove pecky cypress selling for $7.50 per linear foot.  I recall years ago talking to a man that recovered “sinker cypress” from rivers, bayous, and swamps in south Louisiana.  This wood was prized for its beautiful color and grain and had little to no peck.  He was cutting the logs into 4/4 (1 in.) boards and selling it for $10 per board ft (green) to contractors in Houston, TX.   He had open orders to provide as much as he could supply!

Peck is actually a condition caused by a fungal attack that leaves long, narrow burrows or cavities in the wood. The fungus attacks mostly older cypress trees from the tree canopy down to the roots. Once the tree is harvested, the fungal attack stops, leaving the beautiful, unique pecky patterns.  Many fungi attack T. distichum trees. The main fungi is Stereum taxodii which attacks the heartwood of living trees.  A few other fungi species and insects will attack cypress heartwood and sapwood but are not responsible for peck.  Perhaps the biggest threat to pecky cypress is nutria which eat young cypress seedlings so they never have a chance to become a merchantable tree – with or without peck.  

Todd Shupe is the President of DrToddShupe.com and is a well recognized expert on wood-based housing and wood science.  Shupe worked as a  professor and lab director at LSU for 18 years and Quality Manager for Eco Environmental (Louisville, KY) for 2 years. He is active in several ministries including his Christian blog ToddShupe.com. Todd is the Secretary of the Baton Rouge District of United Methodist Men, Database Coordinator for Gulf South Men, and volunteer for the Walk to Emmaus, Grace Camp, Iron Sharpens Iron, Open Air Ministries, HOPE Ministries food pantry. Todd is currently preparing to be a Men’s Ministry Specialist through the General Commission of United Methodist Men.