Showing papers by "Benny K.G. Theng published in 1999"

An improved method for determining the specific surface areas of topsoils with varied organic matter content, texture and clay mineral composition

Abstract: Summary Measuring the specific surface area (SSA) of soils that contain much organic matter (OM) is problematic. The adsorption of p-nitrophenol (pNP) from xylene at room temperature yielded realistic values for the SSA of a wide range of clays, oxides and subsoils. Here we have extended the same measurement to some topsoils with varied OM content, texture and clay mineral composition. Specifically, we have compared the surface areas measured by adsorption of N2, and, applying the BET equation, with the values obtained by adsorption of pNP, before and after treatment of the samples with hydrogen peroxide. In all instances, the removal by H2O2 of organic matter – albeit in part only – led to a marked increase in the SSAs measured by nitrogen because of the exposure of micropores previously blocked or covered by OM. The surface areas measured by pNP were appreciably larger than those obtained by the standard BET equation, and showed little change after removal of organic matter. However, the surface area of two smectite-rich samples measured by pNP increased substantially after peroxidation, presumably because smectite crystals decomposed during treatment with H2O2. The results suggest that, under the experimental conditions used, pNP could diffuse without hindrance into and through organic matter, enabling it to adsorb on to micropore surfaces within clay aggregates (domains). In keeping with this suggestion, the relation between the surface areas measured by pNP and the corresponding values calculated from the clay and OM contents, and clay mineral composition, of the soils was close to 1:1. An even stronger relation was observed between the measured and calculated values for cation exchange capacity.

A 13C‐NMR study of the interactions of soil organic matter with aluminium and allophane in podzols

Abstract: Summary The stabilization of organic matter in soil by interaction with aluminium (Al) or allophane is important in maintaining soil quality, and in retarding the decomposition of soil organic matter. Complexation of Al by soil organic matter may also ameliorate Al toxicity. Here we use 13C-NMR spectroscopy to assess the interaction of soil organic matter with both Al and allophane in two poorly drained podzols containing only trace amounts of iron. The 13C-NMR spectrum of the subsoil of the allophane-rich One Tree Point podzol shows an intense peak at 179 p.p.m., assigned to carbon in carboxylic acids. This peak shifts to 177 p.p.m. after removal of allophane (11% of the soil mass) by treatment with HF. We infer that the carboxyl groups in the organic matter are bonded to structural Al on the surface of allophane spherules. In the non-allophanic Te Kopuru podzol, on the other hand, the organic matter apparently interacts with Al ions in the soil solution. This soil also has more aromatic carbon and fewer carbons in carboxyl and carbohydrate structures than the allophanic sample. There is an indication that allophane stabilizes carbohydrate groups as well as carboxyl groups.

Adsorption of some heavy metals by natural zeolites : XPS and batch studies

Abstract: The adsorption of some heavy metal ions by mordenite and clinoptilolite has been investigated using batch techniques and X‐ray photoelectron spectroscopy (XPS). At 10‐5 M of Pb, Cu, Cd, and Zn, and in the presence of 10‐3 M Ca as a competing cation, the preferential sequence of adsorption was Pb > Cu > Cd > Zn for mordenite, and Pb > Cu > Zn > Cd for clinoptilolite. The adsorption capacities and removal efficiencies of the zeolites for the two highly toxic heavy metals, Cd and Pb, were also determined at a low‐to‐medium concentration range (10‐6 to 10‐3 M), and at a zeolite:solution ratio of 50:30 (mg:mL), in competition with 10‐3 M of Ca. Below 10‐4 M, both mordenite and clinoptilolite removed Pb from the solution almost completely. As Pb concentration increased, removal efficiency decreased. However, the zeolite samples (particularly mordenite) were not effective in reducing Cd concentrations to the legal μg/L level. Solution pHs and the photoelectron binding energies of adsorbed Pb(4f7/2) and ...

Adsorption of DL-alanine by allophane; effect of pH and unit particle aggregation

Abstract: The adsorption of DL-alanine at pH 4, 6 and 8 by a soil allophane has been determined Two sets of experiments were carried out: (1) in which the allophane had been kept in a moist state throughout; and (2) in which the mineral had previously been dried at 50 degrees C In both instances, the adsorption isotherms showed three distinct regions as the concentration of alanine in solution was increased: (1) an initial, nearly linear, rise at low equilibrium concentrations; (2) a levelling off to a plateau at intermediate concentrations; and (3) a steep linear increase at high concentrations For comparable concentrations of alanine in solution, adsorption decreased in the order pH 6 > pH 8 > pH 4 Irrespective of pH, however, more alanine was adsorbed by the "wet" allophane than by its "dry" counterpart These observations are interpreted in terms of the morphology and aggregation of allophane unit particles together with the pH-dependent charge characteristics of allophane and alanine The results are compared with published data on the adsorption of alanine by montmorillonite