Germanium speciation study in soil from an electronic waste processing plant area

Abstract

PurposeGermanium (Ge) is known as a Technology Critical Element (TCE) and has been widely used in electronic and industrial products. Waste electronic and electrical equipment (WEEE) containing germanium goes to WEEE treatment plants. The transfer of Ge in the environment makes it necessary to get to know its mobility, reactivity, and chemical transformations in soil. The objective of this research was to develop a methodology for germanium speciation in soil under pressure from storage, processing, and recovery from electrowaste.Materials and methodsThirty soil cores (30 cm long) were collected from an area around a WEEE plant, using a Humax soil sampler. Soil magnetometry methods were used for the first time during the determination of soil sampling points for germanium. After basic physicochemical analysis (pH, Eh, total element concentration using the ICP-MS technique), soil samples were prepared for germanium speciation. The optimisation and validation of a methodology for determining Ge species in easily-leached fractions of soil collected from areas around an electrowaste plant, was studied using Ion Chromatography-Inductively Coupled Plasma-Mass Spectrometry (IC-ICP-MS). Chromatographic conditions were optimised, taking soil matrix effects into account. Optimised Ge extraction from the soil included: extraction time, type of extractants, extraction support using shaking, and ultrasound.Results and discussionThe Ge species (Ge(IV), monomethylgermanium (MMGe), and dimethylgermanium (DMGe)) were successfully separated after 12 min on a Dionex IonPac AS9-HC column with ammonium nitrate and potassium sodium tartrate as an elution phase. The highest extraction efficiency was achieved by using 100 mM NH4NO3 with 1 mM potassium sodium tartrate as an extractant, that washes out Ge from soils within 4 h. In most cases, the soils contained a Ge(IV) form. Germanium methyl derivatives were only found in a few soil samples. Our research showed that germanium concentration in the studied area was as high as 7.64 mg.kg−1, with an average concentration of 3.51 mg.kg−1. The results allowed the creation of a correlation matrix, which identified many strong correlations.ConclusionThis research confirmed the impact of a WEEE plant on the increase of the Ge content in topsoil, when in direct proximity. Increased germanium content occurred in soil samples located north of the emitter, which is consistent with the prevailing wind direction. The study confirmed that the soil magnetometry method is applicable for detecting TCE. Soil samples with the highest content of germanium had a very high magnetic susceptibility and there is a correlation between these parameters.