Analysis of a room temperature partial extraction technique for heavy metals from soils

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Virginia Polytechnic Institute and State University


A room temperature procedure for the partial extraction of heavy metals from soils was investigated in order to find an optimum combination of acid type, acid strength and digestion period. Hydrochloric and nitric acids were compared. The optimum set of variables would produce a maximum amount of adsorbed metal extraction, with a minimum amount of damage to the soil crystal structures, in the shortest possible time span. Samples were analyzed for aluminum, iron, lead, manganese and zinc. In addition, the amounts of metals extracted by the room temperature procedure were compared with the amounts of metals obtained from both a total extraction and a partial extraction procedure involving heat. The chosen optimum combination technique was performed on a known metals trend area.

No clearly optimal combination of acid strength and digestion time was found which would be applicable to varying types of soils; statistical analysis yielded a compromise point of 1.4N hydrochloric acid and 10.5 hour digestion period, as the most suitable combination. This combination of variables proved suitable since predicted results were obtained from the known metals trend area. Nitric acid was eliminated due to the acid’s lower reactivity. Room temperature extractions using strong acids at extended contact times were found to attack silicate minerals, but solutions stronger than have previously been used may be utilized without damage to the soil structure. Extractions utilizing heat and concentrated acids were too destructive to be considered true partial extractions.