THE SEPARATION OF NEPTUNIUM AND PLUTONIUM FROM NITRIC ACID USING n-OCTYL(PHENYL)-N,N DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE EXTRACTION AND SELECTIVE STRIPPING†

The extraction of neptunium and plutonium in several oxidation states was studied as a function of nitric acid concentration for 0.1M n-octyl(phenyl)-N, N-diisobutylcarbamoyl -methylphosphine oxide in 1.4M tributylphosphate with dodecane diluent. Np(V) is only weakly extractable over the range of acid concentrations studied while Np(IV) and Np(VI) are highly extractable. Pu(IV) and Pu(VI) are also highly extractable while Pu(III) was extracted but with lower efficiency. An Fe(II) reductant was used to reduce neptunium to Np(IV) and plutonium to Pu(III) for the initial extraction. Pu(III) was then stripped with dilute HNO₃ in the presence of a holding reductant leaving the Np(IV) in the organic phase. Neptunium may then be recovered to an aqueous phase with one of a number of complexing agents.     

Amides as Phase Modifiers for N,N′-Tetraalkylmalonamide Extraction of Actinides and Lanthanides from Nitric Acid Solutions

Abstract

The N,N′-tetraalkylmalonamides are a class of compounds under development for transuranic (TRU) separations under high nitric acid conditions. There are several issues that challenge the further development of these ligands. One is the development of improved synthetic procedures that lend themselves to commercial scale-up. Another major issue is the third-phase formation that occurs when the N,N′-tetraalkylmalonamides are contacted with medium-to-high nitric acid concentrations in hydrocarbon solvents. To address the synthesis issue we have developed a new synthetic approach for preparing these materials. Third-phase formation can be eliminated by addition of diluent modifiers such as tributylphosphate (TBP). TBP is inappropriate if a nonphosphate-containing process stream is required. Amides have been proposed as alternatives for TBP in a variety of applications because of their ease of synthesis and the variety of substituents that can be generated. We have been able to develop an amide phase-modified system that extends the working process range of alkylmalonamides (0.5 M) in dodecane (unbranched hydrocarbon) from 3.5 M to 7.5 M nitric acid and in Isopar H (branched hydrocarbon) from 4.0 M to 10.0 M nitric acid using 1.0 M di-2-ethylhexylacetamide/0.5 M alkylmalonamide. The K_d values were comparable to extraction with alkylmalonamide in Isopar H or hydrogenated tetrapropylene (TPH) solvents. The overall extraction system was more robust than the phase-unmodified system allowing for greater temperature and acid concentration fluctuations without third-phase formation.     

Development and Testing of Srex Flowsheets for Treatment of Idaho Chemical Processing Plant Sodium-Bearing Waste Using Centrifugal Contactors

Abstract

Laboratory experimentation has indicated that the SREX process is effective for partitioning ⁹⁰Sr from acidic radioactive waste solutions located at the Idaho Chemical Processing Plant. A baseline flowsheet has been proposed for the treatment of sodiumbearing waste (SBW) which includes extraction of strontium from liquid SBW into the SREX solvent (0.15 M 4′,4′ (5′)-di-(tert-butyldicyclohexo)-18-crown-6 and 1.2 M TBP in Isopar L®), a 0.01 M nitric acid strip section to back-extract components from the loaded solvent, and a 2.0 M HNO₃ solvent acidification section to equilibrate the solvent with HNO₃ prior to recycle to the extraction section. The flowsheet was designed to provide a decontamination factor (DF) of >10³ which will reduce the ⁹⁰Sr activity in the waste solution to below the NRC Class A LLW limit of 0.04 Ci ⁹⁰Sr/m³. SREX flowsheet testing was performed using sixteen stages of 5.5-cm diameter centrifugal contactors. The behavior of stable Sr and other components which are potentially extracted by the SREX solvent were evaluated. Specifically, the behavior of the matrix components including Pb, K, Hg, Na, Ca, Zr, and Fe was studied. The described flowsheet achieved 99.98% Sr removal (DF=4250) with one cycle of SREX. Potassium and Zr were partially extracted into the SREX solvent with 35% and 21%, respectively, exiting in the strip product. Sodium, Ca, and Fe were essentially inextractable. Lead was determined to extract and accumulate in the SREX solvent and in the strip section. As a result, a Pb precipitate formed in the strip stages of the contactors. Mercury was also determined to extract and accumulate in the SREX solvent.     

THE EXTRACTION OF Am(III) FROM NITRIC ACID BY OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE - TRI-n-BUTYL PHOSPHATE MIXTURES

Abstract

The extraction behavior of Am(III) from nitric acid by octy1(phenyl)-N,N-diisobutylcarbamoyl methyphosphine oxides, OØD[IB]CMPO, in the presence of tributylphosphate, TBP, has been studied using diethylbenzene, decalin, and normal aliphatic hydrocarbon diluents. Relative to ØD[IB]CMPO alone, mixtures of TBP and OØD[IB]CMPO show a slight enhancement in the extraction of Am(III) from nitric acid solution above 2 M and a moderate decrease in extraction for lower acid concentrations. The net effect of TBP addition to OØD[IB]CMPO (as well as other selected carbamoyl methylphosphoryl extractants) is a relative insensitivity of the distribution ratio of Am(III) to HNO₃ concentration in the range of 0.5 M to 6 M and facilitated stripping of Am(III) with dilute acid. Since a continuous variation study of Am(III) extraction using mixtures of ØOD[IB]CMPO and TBP at a fixed total concentration revealed no evidence of a mixed complex, the TBP appears to be behaving primarily as a phase modifier

The most significant benefit gained from addition of TBP to ØD[IB]CMPO is the increased metal ion loading capacity and extractant compatibility with alicyclic and aliphatic diluents. The use of TBP to overcome phase compatibility with other bifunctional extractants of the carbamoylmethylphosphoryl type and the use of other phase modifiers with ØD[IB]CMPO have also been investigated.     

RADIOLYSIS OF DIISODECYL PHOSPHORIC ACID AND ITS EFFECT ON THE EXTRACTION OF NEPTUNIUM

Radiolysis of diisodecyl phosphoric acid (DIDPA) in n-dodecane containing tributyl phosphate (TBP) was examined by analyzing concentrations of acidic extractants and H₃PO₄, and its effect on the extraction of neptuniua was studied froi the aspect of the extraction rate. For the solvent containing 0.5 fi DIDPA and 0.1 1 TBP Irradiated in the absence of HNO₃, G-values for degradation of DIDPA and for production of dibutyl phosphoric acid (DBP)were found to be 0.47 and 0.14, respectively. For the solvent irradiated in stationary contact with 0.5 M HNO3, G-value for DIDPA degradation was found to be 0.78, which ras 1.7 tines larger than the value for the solvent irradiated in the absence of HNO₃.     

COMPARISON OF CATION EXCHANGE RESINS FOR RECOVERING AMERICIUM AND PLUTONIUM FROM CHLORIDE SALTS

ABSTRACT

Macroreticular and microreticular cation exchange resins were compared for their capability of recovering americium and plutonium from solutions of calcium, magnesium, potassium, and sodium chlorides. Americium and plutonium breakthrough capacity and elution behavior of the resins were determined. Of the resins tested, Dowex MSC-1 was selected as the most efficient because of its favorable capacity and excellent elution behavior. Actinide eluting agents were also studied. More concentrated (9.0M) nitric acid was found to elute plutonium faster than 7.0MHNO₃used previously while 7.0MHNO₃-0.1MNaNO₂eluted americium fastest.     

Sorption Capacity of Ferromagnetic Microparticles Coated with CMPO

Abstract

Magnetically assisted chemical separation (MACS) was developed at Argonne National Laboratory as a compact process for reducing the volume of high-level aqueous waste streams that exist at many U.S. Department of Energy sites. In the MACS process, ferromagnetic particles coated with solvent extractants are used to selectively separate transuranic nuclides and heavy metals from aqueous wastes. The contaminant-loaded particles are recovered from the waste stream by using a magnet. For the recovery of transuranic species the extractant used is octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in tri-n-butyl phosphate (TBP). To better understand the extraction chemistry of this solvent/particle system, europium was used to monitor the sorption capacity of the MACS particles for lanthanides and actinides. Europium concentrations varying from 10^?7 M to 10^?1 M were prepared with 3M NaNO₃ in 0.1M HNO₃. Neutron activation analysis was used to measure the concentration of europium. The sorption capacity was evaluated, along with the sorption isotherms to simulate multiple contact stages. The maximum absorption capacities obtained was 0.62 mmol/g. The adsorption models of Langmuir and Freundlich and the extended Langmuir model of Brunauer, Emmett, and Teller (BET) were fitted to the data. The best correlations were obtained from the Langmuir and BET models, a result that supports a monolayer adsorption mechanism. The Langmuir and BET models suggested a loading capacity of 0.33 mmol/g and 0.25 mmol/g, respectively. The Freundlich model results support favorable metal loading with a 1/n value of 0.3.

     

Solvent Extraction Chemistry and Kinetics of Zirconium

Abstract

The solvent extraction behavior of zirconium in the HN03-tributyl phosphate (TBP) system can be explained based on the existence of four principal aqueous species, Zr⁴⁺, ZrOH³⁺, Zr₃(OH)⁸⁺ ₄, and oxo-polymers. The Zr⁴⁺ and ZrOH³⁺ species are extractable and are in equilibrium with inextractable Zr₃(OH)⁸⁺ ₄. The oxo-polymers are formed by heat, are-inextractable, and are not: in equilibrium with the other species. The aqueous equilibria and their equilibrium quotients have been previously determined. In the present study, these equilibria were used along with both tracer and macro zirconium concentrations (oxo-polymers excluded by extraction and back scrubbing) to determine the distribution equilibrium constants for both the Zr⁴⁺ and ZrOH³⁺ ions. The four equilibrium constants give excellent fits to both tracer and macro-zirconium distribution data.

The concentrations of the extractable zirconium species which are calculated from the equilibria have been used to begin examining the extraction kinetics of zirconium in the HNO₃-TBP system. In relatively concentrated nitric acid, approximately 3 M and greater, Zr⁴⁺ ion predominates, and the rate of extraction of zirconium increases as approximately the second power of the TBP concentration. In low acid (1 M and less) ZrOH³⁺ ion predominates, and the rate of extraction of zirconium increases as approximately the third power of the nitrate concentration. This is in significant contrast with the behavior of uranium, which shows only a small dependence of the extraction rate on TBP concentration, and no dependence on nitrate concentration. This suggests that operation of a kinetic separations system at low TBP and nitrate concentrations will significantly improve separations over those achieved at equilibrium.     

Laboratory-Scale Counter-Current Centrifugal Contactor Demonstration of an Innovative-SANEX Process Using a Water Soluble BTP

In this paper the development and laboratory-scale demonstration of a novel “innovative-SANEX” (Selective Actinide Extraction) process using annular centrifugal contactors is presented. In this strategy, a solvent comprising the N,N,N’,N’-tetraoctyldiglycolamide (TODGA) extractant with addition of 5 vol.-% 1-octanol showed very good extraction efficiency of Am(III) and Cm(III) together with the trivalent lanthanides (Ln(III)) from simulated Plutonium Uranium Refining by Extraction (PUREX) raffinate solution without 3^rd phase formation. Cyclohexanediaminetetraacetic acid (CDTA) was used as masking agent to prevent the co-extraction of Zr and Pd. An(III) and Ln(III) were co-extracted from simulated PUREX raffinate, and the loaded solvent was subjected to several stripping steps. The An(III) were selectively stripped using the hydrophilic complexing agent SO₃-Ph-BTP (2,6-bis(5,6-di(sulfophenyl)-1,2,4-triazin-3-yl)pyridine). For the subsequent stripping of the Ln(III), a citric acid based solution was used. A 32-stage process flow-sheet was designed using computer-code calculations and tested in annular miniature centrifugal contactors in counter-current mode. The innovative SANEX process showed excellent performance for the recovery of An(III) from simulated High Active Raffinate (HAR) solution and separation from the fission and activation products. ≥ 99.8% An(III) were recovered with only low impurities (0.4% Ru, 0.3% Sr, 0.1% Ln(III)). The separation from the Ln(III) was excellent and the Ln(III) were efficiently stripped by the citrate-based stripping solution. The only major contaminant in the spent solvent was Ru, with 14.7% of the initial amount being found in the spent solvent. Solvent cleaning and recycling therefore has to be further investigated. This successful spiked test demonstrated the possibility of separating An(III) directly from HAR solution in a single cycle which is a great improvement over the former multi-cycle strategy. The results of this test are presented and discussed.     

Supported Extractant Membranes for Americium and Plutonium Recovery

Abstract

Solid supported liquid membranes(SLM) are useful in transferring and concentrating americium and plutonium from nitrate solutions. Specifically, DHDECMP (d ihexyl-N, N-diethylcarbamoyImethylphosphonate) supported on Accurel or Celgard polypropylene hollow fibers assembled in modular form transfers >95% of the americium and >70% of the plutonium from high nitrate (6.9 M), low acid (0.1 M) feeds into 0.25 M oxalic acid stripping solution. Membranes supporting TBP (tri-n-butylphosphate) also transfer these metal ions. Maximum permeabilities were observed to be 1 × 10^?3 cm sec^?1, similar to the values for other systems. The feed:strip volume ratio shows an inverse relationship to the fraction of metal ion transferred. Cation exchangers may be used to concentrate americium from the strip solution.     

DEGRADATION OF TRUEX-DODECANE PROCESS SOLVENT

The hydrolysis and radiolysis of TRUEX-dodecane process solvent (0.2 M octyl(phenyl)N,N-diisobutycarbamoylmethylphosphine oxide (CMPO)-1.2 M tributylphosphate (TBP) in n-dodecane) has been Investigated in a series of experiments conducted in a biphasic mode involving contact with aqueous nitric acid solutions. The stability of the principle extractant (CMPO) is observed to be considerably greater than that reported previously for similar studies in chlorinated diluents. The concentration profiles for the degradation products determined by capillary gas chromatography have been successfully fit assuming pseudo-first order kinetics and mechanistic information derived from these fits.     

Development of a New Flowsheet for Co-Separating the Transuranic Actinides: The “EURO-GANEX” Process

A flowsheet for a novel GANEX (Grouped ActiNide EXtraction) process has been tested in a spiked flowsheet trial in a 32 stage plutonium-active centrifugal contactor rig with a simulant feed that contained 10 g/L plutonium as well as some fission products and other transuranic actinides. The solvent system used was a combination of 0.2 mol/L N,N,N’,N’-tetraoctyl diglycolamide (TODGA) and 0.5 mol/L N,N’-(dimethyl-N,N’-dioctylhexylethoxy-malonamide (DMDOHEMA) in a kerosene diluent that co-extracted actinides and lanthanides. Actinides were subsequently selectively co-stripped away from the lanthanides using a sulphonated and, therefore, hydrophilic bis-triazinyl pyridine (BTP) complexant in conjunction with acetohydroxamic acid (AHA). Plutonium and americium recoveries were high with decontamination factors across the strip contactors of ?14,000 and ?390, respectively. However, approximately 30% of neptunium was lost to the aqueous raffinate which was due to recycling within the first extract-scrub section causing a large build-up of neptunium. Some accumulation of strontium was also observed but in this case it was fully directed to the raffinate stream. In the stripping section, a small fraction of europium (taken as a model lanthanide ion), ca. 7%, was found in the actinide product stream. Modelling of selected data using the PAREX code has shown that even with a relatively simplistic treatment, reasonable agreement between modelling and experiment can be obtained, giving confidence in the use of modelling to refine the GANEX flowsheet design prior to further testing with irradiated fast reactor fuel.     

Mercury Extraction By The TRUEX Process Solvent: III. Extractable Species And Stoichiometry†

ABSTRACT

Mercury extraction from acidic aqueous solutions by the TRUEX process solvent, 0.2 M n-octyl(phenyl)N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), 1.4 M tributylphosphate (TBP) in n-dodecane, has not been extensively examined, Research is currently in progress at the Idaho Chemical Processing Plant to evaluate the TRUEX process for actinide removal from several acidic waste streams, including liquid sodium-bearing waste (SBW), which contains significant quantities of mercury. Reactions for two mercury species, HgCl₂ and HgCl₄ ^?2, are reported. Classical slope analysis techniques were utilized to evaluate the stoichiometric coefficients of each Hg species independently for both CMPO and TBP. The slope analysis results indicate that even the HgCl₄ ^?2 species extracts as HgCl₂. The results also indicate that 1.9 to 2.2 moles of CMPO and 1.5 to 1.81 moles of TBP are required per mole of HgCl₂ extracted. A generic equation for mercury extraction into CMPO or TBP has been shown to be:

where x = 2 or 4, y = 0 or ?2, E = CMPO or TBP, a = the experimentally determined CMPO or TBP stoichiometry, and over lines indicate organic species. Equilibrium constants for HgCl₂ species were determined to be 295 when extracted by CMPO and 18.2 when extracted by TBP. Equilibrium constants for the HgCl₄ ^?2 species were found to range between 5.8 and 12.0 for the CMPO reaction and 0.13 to 0.27 with TBP.     

Evaluation of the SREX Solvent Extraction Process for the Removal Of 90Sr and Hazardous Metals from Acidic Nuclear Waste Solutions Containing High Concentrations of Interfering Alkali Metal Ions

Abstract

The SREX process, which was developed at Argonne National Laboratories, has been evaluated for its effectiveness for the decontamination of radioactive liquid waste at the Idaho Chemical Processing Plant located at the Idaho National Engineering Laboratory. The extraction solvent consists of 0.15 M 4′,4′,(5′)-di-(t-butyl-dicyclohexo)-18-crown-6 in either 1.2 M TBP/Isopar L®. Suppressed extraction due to matrix interferences limits D_Sr values to the range of 3-4 in batch extraction experiments. The SREX solvent has been shown to be effective in the removal of non-radioactive Pb from liquid wastes, in addition to the extraction of ⁹⁰Sr. The information from this study has been used to develop a proposed flowsheet for the treatment of liquid waste in centrifugal contactors.     

Kilogram-Scale Purification of Americium by Ion Exchange

Abstract

Sequential anion and cation exchange processes have been used for the final purification of ²⁴¹Am recovered during the reprocessing of aged plutonium metallurgical scrap. Plutonium was removed by absorption on Dowex 1, X-3.5 (30–50 mesh) anion exchange resin from 6.5–7.5 M HNO₃ feed solution. Following a water dilution to 0.75–1.0 M HNO₃, americium was absorbed on Dowex 50W, X-8 (50–100 mesh) cation exchange resin. Final purification was accomplished by elution of the absorbed band down 3 to 4 successive beds of the same resin, preloaded with Zn²⁺, with an NH₄OH buffered chelating agent.

The recovery of mixed ²⁴¹Am?²⁴³Am from power reactor reprocessing waste has been demonstrated. Solvent extraction was used to recover a HNO₃ solution of mixed lanthanides and actinides from waste generated by the reprocessing of 13.5 tons of Shippingport Power Reactor blanket fuel. Sequential cation exchange band-displacement processes were then used to separate americium and curium from the lanthanides and then to separate ～60 g of ²⁴⁴Cm from 1000 g of mixed ²⁴¹Am-²⁴³Am.     

THE EXTRACTION OF SELECTED ACTINIDES IN THE ( III) (IV) AND ( VI) OXIDATION STATES FROM HYDROCHLORIC ACID BY Oπ D( iB) CMPO: THE TRUEX-CHLORIDE PROCESS∗

The extraction of tetravalent Th, Np, and Pu and hexavalent U from hydrochloric acid was studied using octyl(phenyl)-N,N-diiso-butylcarbamoylmethylphosphine oxides, 0π D(iB)CMP0 or CMPO, dissolved in tetrachloroethylene (TCE). A 0·5 MCMPO solution in TCE was found to be an extremely effective extractant for the tetravalent actinides and U(VI) from moderate to concentrated HC1. Extractant dependencies of the distribution ratios of Th(IV), U(VI), and Pu(IV) were 3rd, 2nd, and 3rd power, respectively, indicating the following species: ThCl₄’3CMPO, UO₂Cl₂2CMP0, and PuCl₄»3CMPO. The distribution ratios of a variety of non-actinide elements, including selected alkali, alkaline earths, Al, transition and post-transition metal ions were also measured from 2 Mand 6 M_ HC1. Based on the distribution ratios of tri-, tetra-, and hexavalent actinides from chloride media, a generic actinide extraction/recovery process was developed for the removal of actinides from chloride salt wastes. The process is called TRUEX-Chloride.     

Degradation of Methyl β-D-Ribopyranoside and Methyl β-D-Xylopyranoside by Oxygen in Aqueous Sodium Hydroxide Solution

Methyl β-D-ribopyranoside (1) and methyl β-D-xylopyranoside (2) were degraded by oxygen (0.682 MPa partial pressure) in 1.25 M sodium hydroxide at 120°C. The degradations of 1 and 2 were similar to the previously reported degradations of 1,5-anhydroribitol (3) and 1,5-anhydroxylitol (4), respectively.⁴ Both hydrogen peroxide and stable organic peroxides were detected in the reactions of 1 and 2. The riboside 1 degraded faster than the xyloside 2. This difference in reactivity is proposed to be a function of the relative acidity of the glycosides. Ionization of hydroxyl groups is postulated to be favored in 1, thus facilitating the initiation of the free radical degradation. The degradations of both 1 and 2 exhibited complex kinetics indicating autoinhibited reactions. In spite of the differences in reactivity, glycosidic bond cleavage occurred in approximately 60% of the degradations for both 1 and 2. C-1 radicals, resulting from abstraction of the anomeric hydrogen atom, are proposed to cause the observed autoinhibition via termination reactions with α-hydroxyhydroperoxyl radicals. However, decomposition of the glycosides via C-1 radicals is not believed to constitute a major degradation pathway since the reactivities of 1 and 2 were essentially the same as the analogous 1,5-anhydroalditols, i.e. 3 and 4, respectively. The major acidic degradation products of 1 and 2 were identical, but were formed in different relative ratios. The major acidic products were methoxyacetic acid, lactic acid, glycolic acid, glyceric acid, a methyl 3-C-carboxyfuranoside, and two isomeric 2-C-carboxyfuranosides.     

NOTE: EXTRACTIVE SEPARATIONS WITH HYDROTROPES

Hydrotropic substances, such as, sodium P-toluene sulfonate, potassium P -toluene sulfonate, sodium P -xylene sulfonate, potassium P-xylene sulfonate, sodium benzoate, potassium benzoate, etc., in aqueous solutions, at relatively high concentrations, have been used successfully to separate mixtures of close boiling point substances like 2,6-xylenol/P-cresol, pheno1/o-chlorophenol, P -chlorophenol/2,4-dichlorophenol, and o-cresol76-chloro-o-cresol, dissolved in a suitable solvent. Very high values of separation factor in the range of 10 to 66 have been realised and this novel method appears to be promising for industrial utilization.     

Gallium Solvent Extraction from Sulfuric Acid Solutions Using OPAP

Abstract

The U.S. Bureau of Mines investigated solvent extraction methods for recovering gallium from sulfuric acid leach filtrates produced from hydrometallurgical zinc residues. These filtrates typically had pH values of 0 to 0.5, too low for effective gallium recovery by traditional extractants. Of the nine extractants tested, octylphenyl acid phosphate (OPAP) was the most effective. Gallium stripping was accomplished using a 1.5 M-H₂SO₄ liquor. A continuous solvent extraction system was designed and operated for 32.4 hr, treating a 0.32 g/L Ga and 20 g/L Fe filtrate. Overall gallium recovery in the system was 94%.     

Effects of Cα -Oxidation in the Fungal Metabolism of Lignin

C_α-Oxidation (benzyl alcohol oxidation) is a prominent reaction in the degradation of lignin by white-rot fungi. This study showed that such oxidation markedly retards metabolism of a nonphenolic β-O-4 model compound, 1-(3-methoxy-4-ethoxyphenyl)-2-(o-methoxyphenoxy)propane-1,3-diol, by cultures of Phanerochaete chrysosporium Burds. Surprisingly, however, selective chemical C_α -oxidation of spruce lignins enhanced their depolymerization by the cultures. Thus the decrease in intrinsic degradability of substructures is more than compensated by another effect of C_α-oxidation in lignin. One possibility is that the oxidation increases the accessibility of the lignin to enzymes by decreasing its steric complexity. This study also revealed that the β-O-4 model, like lignin in wood, is degraded in part via C_α-oxidation by P. chrysosporium. Reduction of the α-carbonyl groups thus formed does not occur. Addition of L-glutamate to ligninolytic cultures completely suppresses their competence to degrade the model compound, as it does their ability to oxidize lignin to CO₂. This result strengthens past evidence indicating that substructure models are metabolized by the same enzyme system as lignin.