Influence of degree of compaction on arsenic and antimony co-contaminated soil stabilization: Geoenvironmental properties and chemical species

Abstract

The current research and engineering practice lack adequate consideration of the influence of degree of compaction (DOC) on the stabilization efficiency and the long-term performance of stabilized contaminated soil. This study investigated the influence of DOC on the characteristics of an iron-based stabilizer amended As and Sb contaminated soil. The stabilizer was labelled as PFSC and was a mixture of polymerized ferric sulfate (PFS) and hydrated lime with a dry mass ratio of 2:1. Various tests were conducted to determine the metalloids leachability (HJ 557), unconfined compressive strength (UCS) (ASTM D1633), and hydraulic conductivity (kw) (ASTM D5084) of stabilized contaminated soil with different DOC (ranged from 75% to 96%). A semi-dynamic leaching test following US EPA Method 1315 was performed on soil specimens to explore the leaching controlling mechanisms and determine the observed diffusion coefficients (Dobs) of metalloids releases when diffusion was the controlling mechanism. The influence of DOC on soil pore characteristics and elements’ valence states were investigated by X-ray computed tomography (CT) and X-ray photoelectron spectroscope (XPS). As the DOC increased, the UCS of soil specimens increased from 4.26 to 43.78 kPa, while the kw decreased form 1.33 × 10−7 to 2.81 × 10−9 m s−1. DOC shows different influences on As and Sb leached concentrations. The mean Dobs for As and Sb released form soil specimen with DOC of 96% were 3 and 2 orders of magnitude lower than that of 75%. CT analysis results indicated the macropore number and macropore size in soil specimens were reduced with the increasing DOC. XPS analysis results suggested compaction promoted the specie transformation of As, Sb, and Fe from As(V) to As(III), from Sb(V) to Sb(III), and Fe(III) to Fe(II)., respectively. The pore filling and chemical specie transformation jointly determined the releases of metalloids from stabilized contaminated soil specimen.