METAL SPECIATION STUDIES ON SEWAGE SLUDGES OF URBAN ORIGIN USING SULFUROUS ACID-SOLUTION SPIKED WITH S-35

Speciation studies on a sewage sludge of urban origin have been carrie d out with sulphurous acid solution (pH 1.5). The insoluble fraction w as sequentially extracted with four organic solvents. The results were compared with those obtained using H2SO4 solution (pH 1.5) as blank. In this way the acid-base effect can be separated from those due to ot her mechanisms. In order to explain the effect of the sulphurous acid solution on the organic matter in the sludge, a sulphurous acid soluti on (pH 1.5) containing S-35 as a tracer was used. Elemental, thermo-ac id gravimetric and spectrophotometric (IR, C-13 NMR, AA) analyses were performed both on the aqueous solutions and on the organic extracts. Differences in patterns of solubilization of the organic matter in the solvents (due both to addition of SO3H groups to double bonds and to breaking up of high molecular mass compounds) indicate that in the slu dge examined the following proportions, copper 25%, zinc 79%. lead 9% and manganese 44% are present as compounds which are either water solu ble or bonded to organic matter. Metals bonded to organic matter are r eleased by an acid-base mechanism at pH 1.5. Almost 30% of the mangane se is present as MnO2. A portion (8%) of the copper cannot be released by acid-base action at pH 1.5 being bonded to organic compounds which contain nitrogen functional groups and which include double bonds in their structure. In this sludge the following proportions, copper 33%, lead 73% and manganese 26% are present as inorganic salts or as organ ic compounds soluble neither in water nor in organic solvents after tr eatment with sulphurous acid solution.