A Novel Continuous‐Flow Sequential Extraction Procedure for Metal Speciation in Solids

Abstract

A continuous-flow extraction system was developed to speed up, facilitate, and improve the accuracy of the chemical fractionation of metals in solid materials. A three-step sequential extraction scheme was used to evaluate the novel system by analyzing calcium (Ca), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in a soil certified reference material (National Institute of Standards and Technology [NIST] SRM 2710). In the proposed system, extraction occurred in a closed chamber through which extractants were passed sequentially. The extracts were collected in a number of subfractions for subsequent name atomic absorption analysis. Apart from the advantages of simplicity, speed, and less risk of the contamination that flow analysis systems usually possess, the continuous-flow system can improve the accuracy of chemical fractionation of metals by sequential extraction. The system ensures that extraction is performed at designated pH values without any need of adjustment. Variation of sample weight to chamber volume ratios from 1:12 to 1:40 had no effect on the extractability of the metals studied. In the extraction of the acid soluble fraction, concentrations of acetic acid in the range 0.11 to 0.5 mol L(-1) had no significant effect on the amounts of metals extracted, except Fe. Increasing the concentration of hydroxylamine in the reducible fraction step from 0.04 to 0.5 mol L(-1) affected the extraction efficiency for Fe, Mn, and Zn. The extraction profile, rather than a single value of extracted concentration, of each element offers additional information about the kinetics of leaching processes and chemical associations between elements in the solid materials.

Extrações sequenciais de chumbo e zinco em solos de área de mineração e metalurgia de metais pesados

“…Tem-se verificado que os elementos de maior mobilidade encontram-se, predominantemente, nas formas químicas solúvel, trocável e ligados a carbonato, enquanto os de baixa mobilidade aparecem ligados às frações óxidos de Fe, Mn, além das frações orgânica e residual (Amaral Sobrinho et al, 1994). Apesar das vantagens do processo de extrações sequenciais em relação apenas à determinação dos teores totais de metais pesados no solo, podem ocorrer problemas de baixa seletividade dos extratores (Shan & Chen, 1993;Shiowatana et al, 2001), redistribuição dos metais durante os processos de extração (Tu et al, 1994;Rakasasalaya et al, 1996) e dependência dos resultados das condições operacionais (Sahuquillo et al, 1999 ao ar e passadas em peneira com malha de 2 mm (TFSA). A textura e as características químicas da TFSA (métodos descritos em Embrapa, 1997;Kummer et al, 2010) e a mineralogia da fração argila (métodos apresentados por Melo et al, 2001Melo et al, , 2002Kummer et al, 2010) das amostras são apresentadas nos quadros 2 e 3, respectivamente.…”

Quick sequential procedure for speciation analysis of heavy metals in soils by supersonic extraction

“…(Chao et al, 1983). Shiowatana and et al have also reported that increasing the concentration of hydroxylamine in the reducible fraction step from 0.04 to 0.5 mol L À1 affected the extraction efficiency for Fe, Mn and Zn (Shiowatana et al, 2001).…”

Sequential element extraction of soils from abandoned farms: an investigation of the partitioning of anthropogenic element inputs from historic land use

“…For steps 1 to 3, the extraction was repeated twice. Multiple extractions have been found to give better recovery than single extractions for exchangeable 39 , 40 and oxidisable 33 fractions, hence the inclusion of a second extraction in this protocol. Two extractions were found necessary in step 2 to maintain the end pH at pH 5.…”