Metals and Metalloid Removal by Colloidal Humic Acid–Goethite: Column Experiments and Geochemical Modeling

Abstract

Core Ideas Humic‐acid‐coated goethite effectively removes cationic metals and As(V) from water. Among five elements, sorption of As(V), Cu, and Zn is favored with higher selectivity. In cation–oxyanion binary systems, As(V) enhanced Zn sorption (synergism). Metals less strongly sorbed are desorbed in mixed contamination due to competition for sorption sites. Multi‐surface complexation model in PHREEQC described As(V), Cu, Cd, Ni, and Zn BTCs. Reactive barriers are proposed to scavenge groundwater contaminants such as metals and arsenate. Their remediation capacity is commonly investigated with sorption data disregarding the complexity of the interactions among elements when faced with mixed contamination. This study was set up to measure interactions during reactive transport of the anionic arsenate As(V) and cationic metals and test if that transport can be modeled with geochemical codes. Sand coated with colloidal humic acid–goethite was the adsorbent in line with field work where these colloidal particles have been injected in situ. Equilibrium batch adsorption experiments showed binding preferences in the order: As(V) ∼ Cu >> Zn > Cd > Ni. Column experiments with single and binary mixtures showed an important synergistic effect of As(V) on Zn sorption but the reverse interaction was not found; this interaction is not included in the PHREEQC geochemical code. The breakthrough curves (BTCs) of mixtures of As(V), Cd, Cu, Ni, and Zn showed that Cd and Ni concentrations in the effluent exceeded those of the influent, an overshooting effect attributed to competition among divalent cations. Simulations with the PHREEQC geochemical code using a surface complexation model for sorption reactions on goethite and humic acids coupled to the transport module successfully predicted the most essential trends of the BTCs, illustrating the potential of these codes to estimate the longevity of the reactive barriers used to remediate mixtures of contaminants. The novel aspect of this work is that a correct reactive transport model in PHREEQC was obtained by only adjusting the number of reactive surface sites of the adsorbent from fitting batch sorption distribution coefficient (Kd) values.

Remediation of zinc-contaminated groundwater by iron oxide in situ adsorption barriers – From lab to the field

“…However, the adsorption capacity was lower compared to the batch incubations. The observations are in agreement with those of ( Montalvo and Smolders, 2019 ; Montalvo et al, 2018 ), who also observed that the adsorption capacities in flow-through systems are lower than in batch systems. A likely explanation for this phenomenon is the contact time of the fluid passing through the column as compared to the reaction time of the adsorption process.…”

“…The pH of the groundwater in the injection zone and downstream was increased to 9.1 during the injection, and decreased with time until the end of the monitoring period. This increase in pH is assumed to significantly enhance adsorption of zinc onto Goethite particles as reported previously ( Mohammadian et al, 2021 ; Montalvo and Smolders, 2019 ; Montalvo et al, 2018 ). The amount of Goethite nanoparticles injected in the pilot was calculated for an active adsorption barrier over ca.…”

“…Competitive sorption of (divalent) cations to Goethite and hence reducing effective adsorption capacities have been reported in the literature ( Goldberg et al, 2007 ; Kratochvil and Volesky, 2000 ). In columns filled with Goethite-coated sand, Montalvo and Smolders (2019) observed highest adsorption affinity for copper followed by zinc, nickel, and cadmium. Continuous inflow of higher affine cations (e.g., copper) will result in a reduced adsorption of cations with lower affinity for Goethite surface sites (e.g., zinc) and hence in an earlier breakthrough.…”

“…Point of zero charge (PZC) of these Goethite nanoparticles has been reported to be <3 ( Tiraferri et al, 2017 ), which is lower than reported PZC of bulk Goethite, which is at pH ~8.0–8.5 ( Cristiano et al, 2011 ; Kosmulski, 2016 ). For more information on the characteristics of the iron oxide nanoparticle used in this study, see Montalvo and Smolders (2019) ; Montalvo et al (2018) ; Velimirovic et al (2020) .…”

Current Understanding of the Use of Alkaline Extractions of Soils to Investigate Soil Organic Matter and Environmental Processes

“…Soil organic matter is a chemically complex, heterogeneous mixture of thousands of biotically and abiotically processed molecules, and this complexity has led to the use of different approaches for studying its reactions in soils. A predominant approach to reducing the complexity has been through the use of an operationally defined, alkaline extraction to isolate SOM on a pH solubility basis into humic and fulvic acids to represent natural organic matter in chemical studies (Hiemstra et al, 2013; Montalvo and Smolders, 2019). These humic and fulvic acids are thought to be primarily high‐molecular‐weight aromatic molecules formed through polyphenol polymerization reactions (Stevenson, 1994; Sparks, 2003) that occur in natural ecosystems.…”