Metal immobilization and nitrate reduction in a contaminated soil amended with zero-valent iron (Fe0)

Abstract

Technologies based on zero-valent iron (Fe 0) are increasingly being used to immobilize metals in soils and remove metals and nitrate from waters. However, the impact of nitrate reduction on metal immobilization in metal contaminated soils has been poorly investigated so far. Here, different concentrations of Fe 0 filings (1%, 2% and 5%; wt%) were applied to a metal contaminated soil. The resulting nitrate reduction and metal (Cd and Zn) immobilization was investigated using a column leaching experiment for 12 weeks. Corrosion of Fe 0 filings and precipitation of Fe oxyhydroxydes (FeOOH) on the surfaces of the filings were observed using SEM-EDS and EMPA-WDS at the end of the experiment. Compared to the untreated soil, total nitrate amounts released were lowered by 47%, 59% and 87% in the presence of 1%, 2% and 5% of Fe 0 , respectively. Concomitantly with nitrate reduction, Cd and Zn concentrations in leachates were strongly alleviated in the presence of Fe 0 , which was partly attributed to the rise of soil pH subsequent to nitrate reduction. More importantly, biotests with Lupinus albus L. revealed that the mechanisms involved in metal immobilization are stable to root-induced acidification. However, Fe 0 was not efficient to reduce Cd concentration in Lolium multiflorum Lam., indicating that root processes other than acidification may re-mobilize metals.

Evaluating the Effectiveness of Nanotechnology in Environmental Remediation of a Highly Metal-Contaminated Area—Minas Gerais, Brazil

“…When Fe 0 of the nucleus of the nZVI particles yields electrons, it turns to Fe 2+ and Fe 3+ , which may pass into solution, remaining in soluble phase for low pH values [14,16,56]. This pH condition was observed in the first days of the test (with pH values < 3 in some samples after 3 days).…”

“…The immobilization of iron is followed by other metallic cations that were in high concentrations in the aqueous phase, such as Zn and Cd. These elements can co-precipitate with iron or be adsorbed on the iron hydroxides (FeOOH, Fe(OH) 3 ) formed on the surface of the nanoparticles, which have a strong retention capacity [13,14,[16][17][18][19]56]. These retention mechanisms occurred approximately after 7 days and may explain the gradual decrease of conductivity values from that day on.…”

“…This work aims to test the effectiveness of an in situ remediation methodology based on the immobilization of these PTEs through the application of zero-valent iron nanoparticles (nZVI). Zero-valent iron (Fe0) has been reported as a successful remediation agent for environmental issues and they are extensively used in soils, e.g., [13][14][15][16], due to its physical and chemical properties, namely high reduction power and non-toxicity. Its application reduces the potential leachability of contaminants, preventing their transport into deeper soil layers, rivers, and groundwater [17].…”

“…At a nanoscale, these particles represent a new generation of effective environmental remediation technologies that may offer unique solutions for the removal or degradation of various chemical pollutants in contaminated groundwaters and soils, including chlorinated organic contaminants, transition metals, and metals in solution [14,16,[20][21][22][23][24][25][26][27]. Zero-valent iron nanoparticles (nZVI) are more effective than macroscale ZVI (mZVI), iron powder, or iron filings under similar environmental conditions [14].…”

Recent Advances in Electrocatalytic Nitrate Reduction to Ammonia: Mechanism Insight and Catalyst Design

“…In recent decades, the metal elements that can be used for electrocatalytic NRA have been widely studied, as shown in Figure a . Notably, except for noble metals, the transition metals (Fe, Cu, Ni, Co, and Ti) were extremely active in the nitrate conversion reaction. − The iron-based, Cu-based, and nonmetallic electrocatalysts have been systematically summarized in the literature. ,, In addition to the elements listed in Figure a, the recently reported nonmetallic boron and main-group p-block metals (Sb, Bi, In, etc.) have also shown great action in the electrocatalytic NRA. , For example, Zhang et al investigated the FeB 2 as a model MBene catalyst.…”