A Complete Closed-Loop CCA- Treated Wood Recycling System Chung-Yun Hse Southern Research Station USDA Forest Service Todd F. Shupe School of Renewable Natural Resources Louisiana State University R. C. Tang School of Forestry and wildlife Science Auburn University

Residential use of CCA-Treated wood has resulted in substantial increasing consumption in recent years

Table 1. Production trends in CCA-treated lumber in the United States. * YearVolume of CCA-treated lumber (Million ft 3 ) CCA consumed (Million punds) *: Chemical Economics Handbook by SRI, Wood Preservatives, March 2000.

Talking Points Disposal problem Recycling Value-added products Closed-loop recycling

The Present It has been estimated that about 5 million tons of spent preservative treated wood is disposed of annually into landfills in the United States (Falk 1997), and most of this was treated with CCA (Cooper 1993; Micklewright 1994).

The Future Cooper (1993) estimated that the future volumes of CCA-treated wood removed from service in the United States would rise from 1 million m 3 in 1990 to 16 million m 3 in metric tons of CCA-treated wood waste disposed in FL in 1996 … and will reach 2700 metric tons by 2016 (Solo-Gabriele and Townsend 1999)

Present situation of treated wood recycling and CCA removal Direct recycling for composite manufacturing Incineration Land-filling Solvent extraction Biological remediation Closed-Loop Recycling System

Closed loop recycling system Reformation Composite products (Poles & Panel Products) Recovered CCA CCA-Free biomass materials Spent preservative-treated wood By productsLiquefied wood

Experimental procedure CCA-wood PEG/glycerin acid Liquefied wood Stirring ( o C, min) Filtration or centrifugation Mixing with acetone/water coagulant/precipitant ( FeSO 4 / Ca(OH) 2 ) IPC analysis

Effect of FeSO 4 content on the removal rates of CCA (Complexing in situ, Ca(OH) 2, 5.94%) Cu CｒCｒ As Cu CｒCｒ As Cu CｒCｒ As

Comparison of removal rates obtained from various complexing agents (Complexing in situ, Ca(OH) 2, 5.94%) FeSO 4 (2.5%)FeCl 2 (2.1%)H 3 PO 4 (3.4%) Removal rate of CCA (%) Cu Cr As Cu Cr As Cu Cr As

Effect of pH on the removal rates of CCA. (Complexing in situ, FeSO4, 2.5%) (0%) (1.98%) (3.96% ) (5.94% ) (7.92%) (2.77%) (3.56% )

Conclusions and Remarks Spent CCA-treated wood had a liquefaction reaction rate similar to the untreated wood The amount of sulfuric acid has little effect on the removal rate The presence of ferrous ions or phosphoric acid in the liquefaction enhances the removal of the heavy metal ions The optimum FeSO 4 dosage for maximum CCA removal is between 2.0 to 2.5% The CCA removal rate increases substantially as the amount of Ca(OH) 2 increased from 1.98% to 5.94% or as pH increased from 2.3 to 9.0. thereafter further increases in either Ca(OH) 2 or pH yielded slightly lower CCA removal ratio. On average, the Cu, Cr, and As were removed by 99.8%, 99.3%, and 98.9% respectively by this approach.

A proposed recycling process for CCA treated wood Solvents (Acetone, MeOH) Liquefaction reactor Mixing tank Precipitation /separation apparatus Recovery apparatus for CCA Sludge CCA-free liquefied wood solution CCA-recovering enhancing additives CCA-wood, liquefaction reagents Coagulant precipitant Aqueous solvent Sulfuric acid Phenolic resin Polyurethane Recovered CCA Recovery apparatus for liquefied wood

Closed-loop Preservative-Treated Wood Recycling System Spent Preservative-Treated Wood Bio- degradable foam Adhesive (novolac, resol) Preservative Pyrolysis gasificantion Reuse as solid wood products Thermochemical conversion Energy conversion (creosote) Bio- remediation Crossarm Composite pole Wood based panel products Liquefaction (CCA) Solvent extraction (steam, sub-and supercritical) CCA free liquefied wood Recovered CCA Direct combustion Bio-fuel, chemical Dechlorination Landfill Process residues (slabs and sawdusts)