Establishment of a selective extraction technique for the separation of iron and manganese oxides and organic materials in the natural surface coating samples (NSCSs)

摘要

The selective extraction procedure applied to the natural surface coatings (NSCSs) developed on glass slides was improved and employed to extract and separate Mn oxides, Fe and Mn oxides and organic materials in the natural surface coating samples (NSCSs) collected directly on shingles in the Songhua River, China. The results show that the effects of selective extraction reagents on residual fractions of Fe and Mn in the NSCSs were invisible, and then Fe and Mn determined by sequential extraction procedure were identified as the total extractable Fe and Mn oxides in place of being determined by 10% HNO3. 0.02M NH2OH·HCl + 0.01M HNO3 could remove almost all of the Mn oxides from the non-residual fractions of NSCSs (from 81.4% to 87.4%) with less effect on Fe oxides ( 17.1%). 0.4M Na2S2O4 (pH 6.0) was effective at extracting Mn oxides existed in non-residual fractions (89.3%-98.0%), and to a less degree, Fe oxides (82.3%-111.9%). And that the effects of NH2OH·HCl and Na2S2O4 extraction on OMs were almost negligible (less than 12.4%). These imply that the selective extraction procedure used in NSCSs developed on glass slides could be successfully applied to selectively separate Mn oxides, Fe and Mn oxides in NSCSs naturally growing on shingles as far as the total extractable Fe or Mn oxides were detected by sequential extraction procedure. Meanwhile, 30% of H2O2 heating at 40℃ in water batch was used to selectively remove organic materials instead of 10% HNO3 which was no selectivity and used to extract Mn oxides, Fe oxides and OMs together, and the results indicate that H2O2 was good at selectively removing organic materials from NSCSs (80.1%-87.4%) with less effect on Fe and Mn oxides extraction (less than 4.8% and 13.0, respectively).