Nanoparticles of noble metals in peat of the Upper and Middle Amur Region

Abstract

Swampy soils of the Upper and Middle Amur Region territory occupy an area of 5663.5 km 2 accounting for 13.6% of the whole territory of the Amur Region. Swampy soils are formed under sphagnum mosses and, partly, sedges. In the zone of deciduous forests, these soils are formed from different grasses. The upper peat-bearing horizon of soils consists of vegetation in the stage of semidecay. This horizon is underlain by a mineral glue layer consequently transforming into rock. About 600 deposits of peat with summary potential resources of 1.3 billion tons are located on the investigated territory [1]. The aim of this work was to study the concentration levels of the following noble metal elements (NMs) in peats of the Amur Region: Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au. Mass shares of NMs were detected in the laboratory of chemical analysis of the Institute of Geology and Nature Management, Far East Division, Russian Academy of Sciences, from 10 g samples after stepwise ashing at temperatures below 600 ° C with a heating speed of 100 ° C per hour. The mass shares of Au, Ag, Rh, Pd, and Pt have been detected by the atomic adsorption method [2, 3]. The kinetic method was used for detecting Os and Ir [4, 5], and the catalytimetric method for Ru detection [6] (the average values are shown in Table 1). Analysis was performed according to the III accuracy category with the maximal error of NM determination amounting to ± 30%. Oxidized forms of NMs are well dissolved in mineral acids that are not oxidants. In contrast, metal forms of NMs are practically insoluble in it. This feature was used for extracting the oxidized forms of NMs by an acid extract. Peat samples of 10 g in weight were processed by a definite amount of strong hydrochloric acid (with a density of 1.19 g/cm 3 ) during 1 hour of mixing. The concentration of the solution was further brought to 2‐3 M of HCl, and then it was heated under a cover up to boiling. The hot solution was passed through the double filter “blue band” with a pore diameter of 1‐2 µ m, and then it was twice washed by a hot solution of 3 M HCl. The acid extract consists of nanoparticles of NMs with dimensions less than 1 µ m and ions of oxidized forms of NMs. The filtrate was analyzed due to the methods of [2‐6]. The concentration of oxidized forms of NMs was determined from the acid extracts by their extraction of the following mixture: 0.025 M paraalkilaniline and 0.05 M diethylhexylditiophosphoric acid in toluene. The oxidized forms of Pt, Pd, Ir, and Os were additionally instrumentally determined with the help of the inversion voltamperometric analyzer TA-4. Thus, the proposed method allows separating ions of the oxidized forms of NMs and their nanoparticles from silicate and organic matrixes and performing their separate determination by instrumental and extracting methods of quantitative chemical analysis. Within the Amur Region, the investigated area con