Influence of solid-liquid separation method parameters employed in soil leaching tests on apparent metal concentration

Abstract

Soil leaching tests are commonly used to evaluate the leachability of hazardous materials, such as heavy metals, from the soil. Batch leaching tests often enhance soil colloidal mobility and may require solid-liquid separation procedures to remove excess soil particles. However, batch leaching test results depend on particles that can pass through a 0.45μm membrane filter and are influenced by test parameters such as centrifugal intensity and filtration volume per filter. To evaluate these parameters, we conducted batch leaching experiments using metal-contaminated soils and focused on the centrifugal intensity and filtration volume per filter used in solid-liquid separation methods currently employed in standard leaching tests. Our experiments showed that both centrifugal intensity and filtration volume per filter affected the reproducibility of batch leaching tests for some soil types. The results demonstrated that metal concentrations in the filtrates significantly differed according to the centrifugal intensity when it was 3000 g for 2h or less. Increased filtration volume per filter led to significant decreases in filtrate metal concentrations when filter cakes formed during filtration. Comparison of the filtration tests using 0.10 and 0.45μm membrane filters showed statistically significant differences in turbidity and metal concentration. These findings suggest that colloidal particles were not adequately removed from the extract and contributed substantially to the apparent metal concentrations in the leaching test of soil containing colloidal metals.

Leaching characteristics of naturally derived toxic elements in the alluvial marine clay layer beneath Osaka Plain, Japan: implications for the reuse of excavated soils

“…Importantly, these results confirm previous reports that the 0.45 µm filter is not sufficient to completely remove suspended particles, which affects evaluations of the mobility of certain toxic elements such as Pb (e.g., Yasutaka et al 2017;Imoto et al 2018;Ito et al 2018).…”

Determining Adsorption Parameters of Potentially Contaminant-Releasing Materials Using Batch Tests with Differing Liquid-Solid Ratios

“…Colloids could have passed through the filter during the liquid-solid separation step, and so may have affected the measured concentrations in the eluate [ 28 , 29 , 30 ]. To confirm the effect of colloids, eluates obtained using a 0.45 μm pore size filter (0.45 MF) were refiltered using a 0.1 μm pore size filter.…”

“…This suggests that in smaller LS conditions, colloids of 0.45 μm or smaller were removed at the first filtration by the cake that formed on 0.45 MF, but in larger LS conditions, such cake did not foam sufficiently to remove the colloids. Subsequent refiltration using 0.1 MF was able to remove colloids of 0.1–0.45 mm, resulting in significant reductions of their concentrations in the eluates [ 28 ]. Furthermore, in LS 300 it may have been difficult to remove colloids of 0.1 μm or smaller during refiltration, as the resulting concentration was higher and the observed variation was larger than those of LS 100.…”

Data of OECD soil and leachate resulting from irrigation with aqueous solution containing trace metals at increasing sodium concentration

“…Leachates were collected daily and divided into two aliquots. No filtration procedure was applied to avoid the removal of analytes bound to colloidal phases [8]. The first aliquot was acidified with 3% HNO 3 for TMs analysis.…”