Organically bound metals

Solvent extraction shows effectiveness in the removal of organic wastes such as PCBs, VOCs, halogenated solvents, and petroleum wastes, but is less effective in removing inorganic compounds.39 The removal of organic contaminants depends on the nature of the extracting solvent. Organic bound metals can become a constituent of the concentrated waste, which is undesirable because it can restrict both disposal and recycle options. 

Hausler, D.W. and Taylor, L.T. (1981) Size exclusion chromatography of organically bound metals and coal-derived materials with inductively coupled plasma atomic emission spectrometric detection. Anal. Chem., 53, 1227-1231. 

Zhang, H. and W. Davison. 2000. Direct in situ measurements of labile inorganic and organically bound metal species in synthetic solutions and natural waters using diffusive gradients in thin films. Anal. Chem. 72 4447 1457. 

The metal phases which are presumed to be sequentially extracted are step 1, soluble, exchangeable and carbonate-bound metals step 2, metals occluded in easily reducible manganese and iron oxides step 3, organically bound metals and sulphides step 4 , metals in non-silicate minerals lattice structure. It is important to emphasise that these metal phases are nominal target only, operationally defined by the extraction used. Consequently, is highly desirable and recommended to refer to the sequentially extracted metal fractions as easily extractable , reducible , oxidi-sable and residual , respectively. 

A question of considerable interest in coal hydroliquefaction chemistry is the amount and nature of "organically bound metals in the coal. One reason for this interest is the observation that when supported metal direct conversion catalysts are used in liquefaction reactors, a primary mode of deactivation is metals deposition Q, 2). In particular, recent work at the Pittsburgh Energy Technology Center (PETC) (4,5) and elsewhere (3) has indicated very high levels of titanium deposition on supported Co Mo catalysts used in the fixed bed continuous reactor system. It has been suggested that the culprits in such deposition are soluble metal species (6 9) The analyses of a Western Kentucky (Homestead) hvBb feed coal and of material deposited between the catalyst pellets in the fixed bed reactor at PETC (4) are shown in Table I. 

The present work which we believe relates to both quantitation and speciation will (1) extend the number of solvents and chromatographic methods which can be employed using this technique, (2) present metal detection limits in a variety of solvents for both direct aspiration and pumped delivery, (3) discuss trace metal quantitative analysis data obtained on pyridine solutions of several SRC s as a function of processing conditions and coal source and (4) describe the isolation of organically bound metal fractions in a SRC process solvent. 

Work to present has demonstrated both the existence of organically bound metals in coal derived products as well as the feasibility for direct detection and quantitation in organic solvents by ICP-AES. Before reliable speciation can be accomplished, better chromatographic separations need to be developed. These include preliminary separation into various fractions by polarity followed by subsequent analysis by HPLC. 

Four types of analyses can be performed in metal determinations, dissolved, suspended, total, and acid extractable metals, based on different sample pretreatment steps. The term total metals includes all inorganically and organically bound metals and requires a vigorous digestion step of the unfiltered sample before analysis. Dissolved metals determination requires filtration of unacidified sample that passes through a 0.45 pm membrane filter. Suspended metals refer to the metals that are retained by a 0.45 pm filter. Acid-extractable metals are determined after the unfiltered sample is treated with hot dilute mineral acid before analysis. 

Organically bound metals and metalloids Toxicity, aquatic biota... 

Fraction 1 is likely to define the actual concentration of metals in soil solution. Fractions 2-4 might be mobilised in the short and medium term by changes in soil chemistry. Fraction 2 is supposed to be easily mobilised from the surface of soil constituents (soil sorptive complex) by changes in pH. Fractions 3 and 5, which represent metals bound to Mn oxides and amorphous Fe oxides, should be sensitive to changes in redox potential. Fraction 4, reflecting the organically bound metals, will probably be mobilised by the decomposition of soil organic matter. Fractions 6 and 7 are expected to be relatively stable, particularly in well-aerated soils, as reaction kinetics of iron oxides and silicates are slow. 

Odermatt, J., Curiale, J., (1991), Organically bound metals and biomarkers in the Monterey formation of the Santa Maria basin, California, Chem. Geol. 91, 99-113. 

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