LAUSR

Abstract The complicated reactions among elemental pollutants and humic substances (HS) in soil matrix are not fully understood. Herein, natural humic acid (HA) was evaluated for its foreseeable in-situ and ex-situ remediation effects on a Typic Torripsamment soil subjected to long-term irrigation with sewage effluents. Humic acid was extracted from Vertic Torrifluvents soil (HA S ), farmyard manure (HA FYM ) and wheat straw (HA WS ). Physicochemical analyses illustrated the higher surface reactivity of HA WS compared to other types. Ecological risk assessment indices showed hazardous soil contamination due to the cumulative impact of potentially toxic elements (PTEs). The extractability of PTEs showed variations in HA-amended treatments. Mobile and/or available fractions of some PTEs (As, Cd, Mn, Ni, Pb and Zn) showed higher extractability compared to the unamended treatment suggesting the potentiality of HA to serve as a washing agent. Other PTEs (Cr, Fe and V) showed less extractability suggesting the immobilization effect of HA. The ex-situ kinetic removal of aqueous PTEs increased sharply, peaked at  ∼ 240 min, and reached equilibrium at 48 h. HA WS showed higher in-situ and ex-situ remediation efficiency compared to other types given the uniqueness of its surface reactivity.Derjaguin–Landau–Verwey–Overbeek (DLVO) theory well-interpreted the behavior of HA transport in sand column, and the actual mobility fitted well with Advection–dispersion–reaction (ADR) model. Attachment of HA onto sand beads occurred via secondary energy minimum, and the mass balance calculations showed recovery values of about 56.7, 48.9 and 44.7% for HA S , HA FYM and HA WS , respectively. In essence, data of this research provide insights for understanding combined washing-stabilization mechanisms involved in PTEs remediation by HA amendments.