Selective leach sampling

The behavior of elements (toxicity, bioavailability, and distribution) in the environment depends strongly on their chemical forms and type of binding and cannot be reliably predicted on the basis of the total concentration. In order to assess the mobility and reactivity of heavy metal (HM) species in solid samples (soils and sediments), batch sequential extraction procedures are used. HM are fractionated into operationally defined forms under the action of selective leaching reagents. 

The authors have set out to attempt to use deep-penetrating geochemical methods, based on fine-grained fraction sampling and selective leaching in exploration for hidden sandstone-type... 

Wide-spaced sampling was carried out in an area of approximately 150 000 km at density of one sample per 100 km (Wang et al. 2007). Soil samples were collected from the weakly cemented sandy horizon at a depth of 20-30cm. The soil samples were subjected to total analysis and selective leaching of mobile metals. Elements were determined by ICP-MS. 

A typical suite of X-ray diffractograms is shown in Fig. 8 for bottom ash samples. Diffraction peaks differ between sample treatments. With bottom ash, a large amorphous background signal is present. Thirty to 40 peaks are selected for analysis in the search match software. As shown in Tables 6 to 8, a number of metal phosphates were found in the treated samples and the treated and leached samples for the bottom ash, scrubber residue, and vitrification dust samples. Apatite family and tertiary metal phosphates are common to both the treated and unleached samples and the treated and leached samples for all three ashes. 

Gross dissolution of the waste can be measured from the loss of weight of the sample or by determination of the appearance in the leaching medium of the major matrix constituent e.g. glass). However, the selective leaching of important fission product elements has been observed in this work to be significantly different from that of the bulk waste matrix. The units normally used to describe leach rates, g/cm day, appear to imply... 

Since selenoamino acids are water-soluble, leaching with hot water has been judged sufficient to recover Se species not incorporated into larger molecules. The sample is homogenized with water, sonicated or heated, and ultracentrifuged. The typical recovery of Se extracted in this way from selected yeast samples is usually ca. 10D20 percent [20, 21], Free selenoamino acids can also be separated by ultraMtration (breast milk) [22]. 

The importance of the total sample dissolution technique mentioned earlier becomes apparent because the detrital phase contains Th and U that is both lattice-bound and adsorbed but in unknown proportions. Bischoff and Fitzpatrick (1991) demonstrated that it is not possible to quantitatively separate these two components by selective leaching. 

Selective leach techniques have become popular in mineral exploration for the treatment of geochemical soil samples. Their popularity stems from the fact that they are considered to extract selectively a particular hydromorphically-transported component of metals in the sample and, as such, show better anomaly-to-background contrasts than do conventional strong acid digestions which dissolve most of the chemical matrix of the soil. 

Titration results available (different NaCI concentrations). Selective leaching of components. PZC at pH 9-10 (pH, dependent of ionic strength and sample treatment). 

Samples of SS 316 stainless steel, exposed to flowing sodium at different temperatures, were exalted for diemical and mechanical property dianges. The threshold oxygen contents in sodium forthe formation of KaCrO when in contact with 316SS, 304SS, D9 alloy, 2.1/4Cr- IMo and 9Cr-lMo steels were calculated. The influence of selective leaching of chromium on the carbon actiwty oC socfium in the loop was assessed by a thermorfynamic model... 

---