Different roles of FeS and FeS2 on magnetic FeSx for the selective adsorption of Hg2+ from waste acids in smelters: Reaction mechanism, kinetics, and structure-activity relationship

Advances in the sources, chemical behaviour, and whole process distribution of Hg, As, and Pb in the iron and steel smelting industry

The Chinese iron and steel industry, with its large production volume and reliance on coal-dominated energy structures and blast furnace/basic oxygen furnace processes, is a significant contributor to heavy metals (HMs) emissions and a potential threat to the environment and human health. This study systematically reviews the sources, chemical behaviour transformations, and whole process distribution of mercury (Hg), arsenic (As), and lead (Pb) throughout iron and steel smelting processes. Coal and iron ore were the major input sources of the three HMs. The chemical transformations of HMs are closely related to temperature changes. During combustion, HMs volatilise, condense in the scrubbing system, and remain gaseous or are removed as products/by-products during flue gas treatment. Sintering was identified as the primary emission source of Hg, accounting for 36.79 % of the total process emissions, with an average emission factor of 108.36 mg/t-CS. The blast furnace process is the main emission source for As and Pb, contributing 75.19 % and 59.10 % of total process emissions, respectively, with average emission factors of 43.82 mg/t-CS for As and 231.16 mg/t-CS for Pb. Throughout the iron and steel smelting process, Hg is primarily released as dust ash and desulfurisation by-products (33.30-76.91 %). As mainly remains in hot rolled steel products (57.60-75.04 %). Meanwhile Pb forms a recycling loop between the sintering and basic oxygen furnace processes, with some Pb being released as blast furnace slag (11.41-79.22 %). The results of this study can provide a scientific basis for the development of future HMs reduction technologies and control strategies. More attentions should be paid to HMs in wastes from the whole process of iron and steel smelting in future policy making.

In situ remediation of mercury-contaminated groundwater through an in situ created reactive zone enabled by carboxymethyl cellulose stabilized FeS nanoparticles

Faced with worldwide mercury (Hg) contamination in groundwater, efficient in situ remediation technologies are urgently needed. Carboxymethyl cellulose (CMC) stabilized iron sulfide (CMC-FeS) nanoparticles have been found effective for immobilizing mercury in water and soil. Yet, the potential use of the nanoparticles for creating an in situ reactive zone (ISRZ) in porous geo-media has not been explored. This study assessed the transport and deliverability of CMC-FeS in sand media towards creating an ISRZ. The nanoparticles were deliverable through the saturated sand bed and the particle breakthrough/deposition profiles depended on the injection pore velocity, initial CMC-FeS concentration, and ionic strength. The transport data were well interpreted using an advection-dispersion transport model combined with the classical filtration theory. The resulting ISRZ effectively removed mercury from contaminated groundwater under typical subsurface conditions. While the operating conditions are yet to be optimized, the Hg breakthrough time can be affected by groundwater velocity, influent mercury concentration, dissolved organic matter, and co-existing metals/metalloids. The one-dimensional advection-dispersion equation well simulated the Hg breakthrough data. CMC-FeS-laden ISRZ effectively converted the more easily available Hg species to stable species. These findings reveal the potential of creating an ISRZ using CMC-FeS for in situ remediation of Hg contaminated soil and groundwater.

One-step synthesis of a core-shell structured biochar using algae (Chlorella) powder and ferric sulfate for immobilizing Hg(II)

Mercury (Hg) pollution poses a significant environmental challenge. One promising method for its removal is the sorption of mercuric ions using biochar. FeS-doped biochar (FBC) exhibits effective mercury adsorption, however may release excess iron into the surrounding water. To address this issue, a novel magnetic pyrrhotite/magnetite-doped biochar with a core-shell structure was synthesized for the adsorption of 2-valent mercury (Hg(II)). The proposed synthesis process involved the use of algae powder and ferric sulfate in a one-step method. By varying the ratio of ferric sulfate and alga powder (within the range of 0.18 - 2.5) had a notable impact on the composition of FBC. As the ferric sulfate content increased, the FBC exhibited a higher concentration of oxygen-containing groups. To assess the adsorption capacity, Langmuir and Freundlich adsorption models were applied to the experimental data. The most effective adsorption was achieved with FBC-4, reaching a maximum capacity (Qm) of 95.51 mg/g. In particular, at low Hg(II) concentrations, FBC-5 demonstrated the ability to reduce Hg(II) concentrations to less than 0.05 mg/L within 30 min. Additionally, the stability of FBC was confirmed within the pH range of 3.8 - 7.2. The study also introduced a model to analyze the adsorption preference for different Hg(II) species. Calomel was identified in the mercury saturated FBC, whereas the core-shell structure exhibited excellent conductivity, which most likely contributed to the minimal release of iron. In summary, this research presents a novel and promising method for synthesizing core-shell structured biochar and provides a novel approach to explore the adsorption contribution of different metal species.