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.

Grain Patterns of Birdseye-Maple Wood

Birdseye-Maple Wood Guitars
Photo courtesy of Dr. Terry Conners

Unique Grain Patterns of Birdseye-Maple Wood

We all love unique grain patterns in wood.  “Figure” refers to the grain pattern of wood on the longitudinal plane of the tree (vertical direction).  Wood with figure displays a unique grain pattern from normal wood of the same species.  The figure of wood is, in part, due to its grain and, in part, due to the cut, or to innate properties of the wood.  Types of figure include “bear scratches,” bird’s eye, blister, burl, curl, ribbon curl, dimple, fiddleback, flame, wide flame, “ghost”, pin stripe, quiltedspalted, and tiger stripe. 

In this blog I want to focus on the unique grain pattern that can be found in sugar maple, which is sometimes called hard maple.  There are many species of maple but they all have the same genus:  Acer.  For sugar maple, I am referring to Acer saccharum.  This species is native to the hardwood forests of eastern Canada and the northern parts of the Central and Eastern United States.   Sugar maple is best known for its bright fall foliage and for being the primary source of maple syrup.  A little known fact is that hard maple has become the most popular choice for wooden baseball bats in major league baseball.  For years, the wood species of choice was ash but that has gradually been declining to hard maple. Most of the maple used for baseball bats comes from forests in Pennsylvania and is carefully harvested, milled, and dried.  Another fun bit of trivia is that hard maple is widely used for basketball courts throughout North America due to its resistance to splintering, light color, durability, and ease of finishing.

Birdseye figure is due to a pattern of indentations in the growth rings. If the wood is split tangentially {i.e., the plane of the split is essentially parallel to the growth rings), conical projections or elevations are revealed, with corresponding indentations on the matching piece.  These projections and indentations extend inward toward the pith, generally beginning in the bark and extending through the wood for an indeterminate number of growth rings.

Birdseye is classified as a “figure related to indented growth rings,” and indeed, close examination of the cross-sectional surface of birdseye reveals that the growth rings do appear to be indented. It is as though a blunt conical instrument were used to cause a localized indentation in the bark, cambium, and wood. These areas contain the same types of cells as found in the surrounding “normal” wood, but the longitudinal cells are not vertically oriented as their counter parts in the normal tissue. Because these projections and indentations generally extend into the bark, standing trees can be easily examined for the presence of birdseye with little physical damage.  Several domestic hardwoods have been reported to display birdseye such as ash, walnut, beech, birch.  Birdseye is most valuable in sugar maple, although it does occur in other species of maple.  Sugar maple with birdseye can be processed into high value veneer and used for caskets, furniture, etc. and milled into lumber for paneling and flooring.

Reference:  Bragg, D.C. and D.D. Stokke.  1994.  Field identification of birdseye in sugar maple (Acer saccharum Marsh.).  USDA Forest Service, North Central Forest Experiment Station.   St. Paul, MN.  Research Paper NC-317.  20 p.

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.

Wood Flooring – Lawsuits, Experience, and Opinions

Photo courtesy of Gene Mall

I love solid wood floors.  I have seen old dilapidated houses bought with a credit card and the floors and paneling salvaged and resold for a tremendous profit.   Studies have shown that patients in hospitals will heal faster when they are in a room with a more natural “feel” than a traditional hospital room.  Part of this natural feel is wood floors (and paneling too).  Wood has an inherent beauty and nostalgic affect, and I think most people appreciate it and enjoy it especially during these complex and busy days we all tend to live.

Wood floors can have problems.  Typically, if you have a wood floor problem, you have a wood moisture content problem.  Each piece of wood is unique and depending on how the piece was sawn will determine if most of the dimensional change is in the thickness or width of the plank.  The most frequent problem is buckling of the floor or excessive gaps between the planks.  Buckling will occur when the moisture content of the boards is significantly increased after the floor is installed.  The boards want to swell but are restrained by adjacent boards and/or mastic and instead will buckle.  This can be due to several factors such as a water leak in the house, poor vapor barrier below the house if the house is on stilts, or failure to acclimate the wood to the equilibrium moisture content of the house before installation.   In my experience, failure to acclimate the wood is often the culprit.  I recall a case years ago in which a homeowner purchased custom wood flooring from a local distributor.  The wood had been kiln dried to 6-8% MC so it was deemed by the installer that acclimation was not necessary.  However, the boards had sat in a non-climate controlled shed for years after they were kiln dried.  I determined that the moisture content of the boards at the time of installation was probably around 18% and gradually decreased to 8% once in service.  This explains why large gaps were appearing between the boards. 

As a home owner, you may be wondering what can you do to prevent wood flooring problems.  I suggest you purchase a moisture meter and randomly check a few of the boards before installation.  It will take you seconds but can potentially save you hours of heart ache down the road.

Shell Rot in Wood Poles

Photo courtesy of Osmose Utilities

All preservative-treated wood poles commonly used in North America are subject to “shell rot” or surface decay below the ground line.  In southern pine poles, which compose roughly 85% of the poles in North America, this type of decay is most common.  Western species such as Douglas-fir and cedar are less susceptible to surface decay.  However; however, only the heartwood of these species are naturally decay resistance.  So, sapwood of neither Douglas fir nor western red cedar is naturally resistant to decay.  Therefore, as these poles age they can be subject to surface decay, though at later stages in life when compared to southern pine.

Wood destroying decay fungi are the most common wood-destroying organisms and they can be found in virtually any environment.  Decay fungi require four elements in order to live and attack wood: air, water, a favorable temperature, and food (in this case, the wood pole).  If you can remove any of these factors, then the fungi cannot live.  These four elements are most prevalent from the groundline to 18 inches below the groundline.   Beyond this depth, the soil becomes more anaerobic and oxygen is limited.  For any wood product, plywood, lumber, etc, the surface of the product has a tremendous effect on the strength.  For poles, the outer two to three inches governs approximately 90% of the strength.  Therefore, it is critical to inspect and protect this part of the pole to preserve the pole’s strength.  I have served as an expert witness on many cases in which a pole has fallen and caused property damage or death and most could be prevented by (1) having a pole inspection program and (2) using remedial preservative treatments at the groundline when an initial problem is detected.

Extending the life of a pole can be accomplished by in-place treatment with remedial preservatives.  In Bulletin 1730B-121, the Rural Utilities Service (RUS) recommends an 8 to 12 year cycle based on the decay conditions of the particular environment where the poles are installed.  Excluding remedial treatments from a pole maintenance program leaves owners with an inspection only program.  This “run to failure” strategy can have significant long-term negative impacts on our natural resources, skilled manpower, financial resources, and it increases the pole owner’s risk with regard to safety and reliability (Osmose 2017).

Externally applied preservatives vary greatly in their active ingredients, environmental profile, efficacy, penetration into a pole, and their ability to remain in the treatment zone so as to control decay for an extended period of time. Selecting an appropriate remedial treatment strategy can save pole owner’s millions of dollars by reducing the number of pole change-outs and reducing the risks associated with pole failures.  Most remedial treatments are applied by brush as a paste or as a bandage, similar to a large band-aid wrapped around the groundline.  The table below is from Freeman (2007).

References:

Freeman, H.M. 2007.  Wood Pole and Crossarm Maintenance and Remedial Treatment:  A State of the Industry Review.  In:  Proceedings of American Wood Protection Association. 103:151-177.  Birmingham, AL.

Osmose.  2017.  http://www.osmose.com/newsletter-2017-q4-restore-not-replace

The Importance of Wood Species Identification

A hand lens is essential to see anatomical properties.

One of the first things you need to understand about wood is variability.  As a biological material it is inherently different than other building products such as steel.  A steel beam has uniform properties throughout the beam and each beam will have essentially the same properties.  A wood beam will not.  Wood properties vary from tree to tree but also within a tree!  For an individual tree, there is a vertical and horizontal profile that corresponds to tree growth in both the vertical (longitudinal direction) and diameter (radial direction).  These changes are most profound in pine trees.  So, this is the reason why when you go to your local lumber yard you have to dig around in the bin to find the board(s) that you want.  They all have the same grade but due to variability they don’t all look the same nor will they all perform the same. 

Species has a great influence on wood properties.  Each species has unique anatomical properties that allow for a trained eye to properly identify the species.  There are a few exceptions.  For example, there are several species that are classified as southern pine.   Botanically a forester can identify these as separate species based on the cones and needles.  However, there is insufficient variation in the wood properties to separate them so they are all sold commercially as southern yellow pine (SYP). 

The main factor that separates wood species is density which is simply mass per unit volume.  Due to anatomical structure, some species have a higher density (oak, hickory) than others (cottonwood, walnut).  You may wonder if they have the same volume, why isn’t the density the same?  Why does the weight vary between species if we take measurements at the same moisture content?  Again, due to the inherent anatomical structure of some species they have a greater amount of wood per unit volume and others have a greater amount of air per unit volume.  If you were to look at an oak species under a microscope you would see thick cell walls with little open spaces (air).   The opposite is true for a low density species.   So, the first step to proper wood utilization is wood species identification.  If you need help with wood species identification for a special project, legal matter, etc., please contact me at tfshupe@gmail.com.

CCA-Treated Guardrail Posts, Piles, and Poles – Good for the Environment and the Economy

Courtesy of Arnold Forest Products Corp.

Our highway and interstate system is a critical component of our nation’s infrastructure and economy.  They are essential for the transportation of goods and services, emergency responders, commuting to work, and family vacations.   It is imperative that our highways provide safe travel for all.  Highway guardrails (see picture) are an important safety component of our highways.   They typically consist of a galvanized metal rail, treated wood block, treated wood post, and fasters.   However, steel blocks and posts can also be used.

Chromated copper arsenate (CCA) has a long history as an EPA approved wood preservative for numerous applications such as posts and blocks used in the guardrail assembly.   Numerous independent studies have shown that CCA is an environmentally safe wood preservative and has very minimal leaching.   Dr. Kenneth Brooks wrote in Pressure Treated Wooden Utility Poles and Our Environment that “pressure treated wood utility poles pose no greater risk to the environment than growing the wheat used to bake your next loaf of bread, and present far less personal risk than driving to your local grocery store to purchase that bread.”  Similarly, Dr. Paul Morris has written “There are environmental risks associated with everything we do and with all of the material used to construct utility structures. For instance, the leaching of zinc from steel utility poles.”

The Treated Wood Council commissioned an independent study of the environmental impacts associated with the national production, use, and disposition of treated wood and galvanized steel highway guard rail posts using life cycle assessment (LCA) methodologies. The results for treated wood compared to galvanized steel guard rail posts were significant (© Treated Wood Council, 2013).

  1. Less Energy & Resource Use

Treated wood highway guard rail posts require less total energy and less fossil fuel than galvanized steel highway guard rail posts.

  1. Lower Environmental Impacts

Treated wood highway guard rail posts have lower environmental impacts than galvanized steel highway guard rail posts in five of six impact indicator categories assessed: anthropogenic greenhouse gas, total greenhouse gas, acid rain, ecotoxicity, and smog-causing emissions.

  1. Offsets Fossil Fuel Use

Reuse of treated wood highway guard rail posts for energy recovery will offset the use of fossil fuel energy and thereby reduce greenhouse gas levels in the atmosphere.

Bottom Line

CCA-treated wood is a critical part of our nation’s infrastructure and economy.  It is safe for the environment and has a long history of EPA approval for both the environment and human exposure.  The alternatives (steel and concrete) are not renewable and require more energy to produce than CCA-treated wood.    Last but not least, CCA-treated wood is more cost effective than the alternatives.   CCA-treated wood is good for the environment and the economy!

Benefits of Wood Utility Poles

Photo courtesy - Dr. Todd Shupe

Our society has become much more environmentally sensitive and responsible in recent years.  Recycling has increased, air and water standards are improved, smoking tobacco is generally prohibited inside most public buildings, etc.  However, a phobia exists regarding wooden poles.  There is nothing particularly aesthetically appealing about a creosote-treated pole that is leaching creosote out onto the adjacent sidewalk as I witnessed today.  However, wooden poles are good for the environment and much better than the alternatives.

Wooden poles are visible along almost every city street and rural highway.  They are essential components of our national infrastructure.  They are impregnated with chemicals that must be toxic to stop degradation from insects and fungi.  Yes, some of these preservatives will leach out into the adjacent soil.  However, wood utility poles are much kinder to our planet than other materials. Independent, science-based life cycle assessments, or LCAs, confirm that preserved wood utility poles use less energy and resources, offset fossil fuel use and have a reduced environmental impact when compared to concrete, steel and fiber-reinforced composite utility poles.

Wood poles are made from a plentiful and renewable resource grown on managed timberlands. Growing trees produces oxygen and when converted into a product, wood stores carbon. Wood poles also help limit the accumulation of greenhouse gases.  Due to the insulating properties of wood, eagles, ospreys and other large birds are able to perch on wood crossarms without danger of electrocution.

Dr. Kenneth Brooks dedicated much of his career to studying the environmental impacts of preservative-treated wood poles.   Some of the key findings of his research are:  (1)  pressure treated wood utility poles pose no greater risk to the environment than growing the wheat used to bake your next loaf of bread, and present far less personal risk than driving to your local grocery store to purchase that bread.  (2) there are environmental risks associated with everything we do and with all of the material used to construct utility structures. For instance, the leaching of zinc from steel utility poles has been documented.  (3)  Utility poles are not continually immersed in water and the actual lifetime losses are likely far lower — perhaps the equivalent of a penny of copper per year for each 20 poles. “

Naturally Durable Wood Species

Many people have the mistaken belief that naturally durable wood species will not rot.   There are a handful of domestic wood species that are classified as naturally durable.   Some of the more common in the US South are sassafras, live oak, Eastern red cedar, catalpa and black locust.   In the West, redwood and Western red cedar offer natural decay resistance, particularly with heartwood lumber.  The heartwood is the darker wood in the center of most trees.  It is higher in chemical compounds that are responsible for decay resistance.  Some species have a heartwood that easily visually detectable and others do not.  

I purchased a swing set made of redwood about 15 years ago.  Over the years, I have replaced many of the parts of the swing set with pressure-treated southern pine.  My replacement pieces continue to perform fine.  However, each year more pieces of the redwood continue to fail due to wood degrading fungi.  Naturally durable wood species are NOT resistant to wood degrading insects and fungi.  They will provide better protection than untreated wood.  The US South has a very harsh environment for exterior wood in ground contact.  Untreated pine field stakes can show failure in as soon as 1 to 2 years.  My redwood deck began showing failure in 5 years for the pieces in ground contact and 7-8 for those above ground. 

There is no substitute for pressure treated wood for exterior applications.  This material is economical, safe, easy to work with and it will perform in excess of 50 years with minimal maintenance.  In the US South there are numerous utility poles that are well in excess of 50 to 80 years of age that are showing no signs of degradation.   For more information on naturally durable wood species please visit https://www.fs.usda.gov/treesearch/pubs/35536

This piece has suffered from internal wood degrading fungi due to its horizontal position in the swingset which allowed water to pool on the surface and elevate the moisture content to make it conducive for fungi attack.
This is a good example of surface weathering. The natural elements have degraded the surface of the board.