Kenneth M. Holtzclaw

Residual metal reactivity of humic acids extracted from soil amended with sewage sludge

Copper, Fe, and Mn were used as probes to investigate residual metal reactivity for humic acid (HA) samples extracted from a loam soil, either non-amended or amended with anaerobically digested sewage sludge for 4, 5, 6, or 7 yr at 90 t ha−1. yr−1. Irrespective of their origin, the HA complexes significant amounts of metal, in forms stable against intense water-leaching, in the order Fe > Cl > Mn. Sludge-amended soil HA adsorbed and retained Fe in amounts greater than HA extracted fron non-amended soil. Metal adsorption occurred mainly by cation-exchange replacement of metals previousl: bound to HA. Water-stable Fe3+-HA complexes prepared in the laboratory were partially stable agains H+ and metal ion exchange reactions, whereas Cu2+ and Mn2+ in laboratory-prepared, water-stabl HA complexes were desorbed almost completely by these two reactions. Electron spin resonance spectra indicated that the laboratory-prepared metal-HA complexes had a chemical composition and molecula structure similar to that of indigenous metal-HA complexes, which were stable against all leachin, and cation-exchange treatments. Although the HA samples showed a maximal metal binding (i.e. saturation) as metal loading of the sludge-amended soil increased, they still exhibited a high residua binding capacity for the three metals used as probes.

Improved selective dissolution method for determining calcite and dolomite in soils

A selective dissolution method for the simultaneous quantitation of calcite and dolomite in soils is proposed. This method, which can be used for soil dolomite contents as low as 0.1% (wt/wt), retains the attractive characteristics of simplicity and nonreliance on specialized or expensive equipment, while reducing interferences from noncarbonate sources of Ca, Mg, and alkalinity inherent in previous extractive methods. The expected relative inaccuracy of the proposed method is 3% of the “true” soil calcite or dolomite content if any Ca contributed by gypsum is accounted for independently and if the content of magnesian calcite in the soil is very low.