Abstract
Four digestion methods were examined for determination of cobalt, nickel, chromium, cadmium, lead, copper, zinc, manganese, iron, potassium, sodium, calcium, and magnesium in municipal compost (refuse/sludge) samples by atomic absorption spectrophotometry. The four methods examined were: (1) dry ashing followed by digestion with aqua regia, (2) digestion with aqua regia, (3) digestion with nitric acid, and (4) digestion with nitric acid followed by treatment of the residual by sulfuric acid and dry ashing. Based on results concerning observed metal concentrations, precision, and recovery of digested standard solutions, dry ashing was found to be an inefficient digestion method, while the other three methods were comparable. Digestion with aqua regia may have a small advantage compared to digestion with nitric acid and digestion with nitric acid followed by dry ashing. Milling of the compost samples prior to digestion improved the precision for the alkali-and the earth-alkali metals but increased the chromium content of the compost because of wear on the milling equipment.

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