Investigation of Ti contamination and transport mechanisms in ferruginous soils: Impacts of ilmenite and rutile processing and immobilization using clay amendments

Abstract

Titanium (Ti) contamination from coastal mining activities poses significant threats to groundwater and soil quality, especially in regions with ferruginous soils (FS). This study investigates Ti transport and immobilization in FS, assessing its natural retention capacity and the enhancement achieved using bentonite, zeolite, and kaolinite amendments. Environmental assessment identified industrial discharge as the primary source, with elevated Ti in soil (271.67 ppm), surface water (0.56 ppm), and groundwater (0.45 ppm), forcing 86 % of households to rely on alternative sources. The 3D flow model demonstrated that FS reduces Ti mobility; however, rising inlet to outlet head differences (6-12 cm) led to increased flow rates (0.1–0.7 cm3/min), resulting in elevated Ti concentrations in wells 2 and 3(8.55 ppm and 7.23 ppm). Ti peaks observed in the wells were the result of desorption following initial adsorption, reflecting the breakthrough pattern. Batch adsorption tests (0–1000 ppm Ti, 25–27 °C, 1:20 ratio, pH-3.9-5.5) revealed chemisorption dominance at low concentrations (K<inf>d</inf> = 28.5 L/kg, K<inf>L</inf> = 33.39 L/kg) and multilayer physisorption at higher loads (q<inf>m</inf> = 11.09 mg/g, K<inf>f</inf> = 88.11 L/kg), modelled using Linear, Langmuir, and Freundlich isotherms. XRD and SEM-EDS confirmed Ti incorporation into stable mineral phases (Al<inf>8</inf>Ti<inf>32</inf>Cl<inf>48</inf>, Fe<inf>4</inf>Ti<inf>2</inf>Cl<inf>7</inf>, Ti<inf>3</inf>O<inf>5</inf>) with increased retention (4.1–7.8 %). Among amendments, bentonite-enhanced FS showed the highest Ti retention (97.5 %, K<inf>f</inf> = 478.5 L/kg) at 10–20 % dosage. This integrated experimental framework is transferable to other heavy metal-affected coastal aquifers, where it supports predictive contaminant transport and groundwater protection strategies aligned with the Sustainable Development Goals. © 2025