Sponge Iron Research Articles

Characterization of Achromobacter denitrificans QHR-5 for heterotrophic nitrification-aerobic denitrification with iron oxidation function isolated from BSIS：Nitrogen removal performance and enhanced SND capability of BSIS

Strain QHR-5, a heterotrophic nitrification-aerobic denitrification bacterium (HNADB) with iron oxidation function, was isolated from biological sponge iron system (BSIS) and identified as Achromobacter denitrificans. The carbon source suitable for growth and nitrogen removal by the strain from the denitrification medium 1(DM1) was investigated. Maximum growth and total inorganic nitrogen (TIN) removal were observed when Seignette salt was the carbon source. Single-factor experiments showed that the highest NO3--N removal performance was achieved when C/N ratio was 17, the shaking speed was 120 rpm, the temperature was 30 ℃, and the pH was 7.0. The heterotrophic nitrification and aerobic denitrification activity with different nitrogen sources (NH4+-N, NO3--N, and NO2--N) showed removal efficiencies of 90.84%, 98.37%, and 60.37%, respectively. With NH4+-N, NO3--N or NH4+-N, NO2--N as mixed nitrogen sources, Strain QHR-5 still showed good denitrification activity. Runs R1 (BSIS) and R2 (BSIS + Strain QHR-5) showed that with higher concentration NO3--N (981.12 mg/L), the TN removal efficiency of R2 increased by 18.32%. Higher TN removal efficiency could be attributed to the aerobic denitrification capability of Strain QHR-5 and the accelerated dissolution of Fe2+ in BSIS due to the iron oxidation function of Strain QHR-5.

Continuous H2S removal from biogas using purple phototrophic bacteria

Biogas from anaerobic digestion requires desulfurisation before its intended use due to the corrosive nature of H2S. Anaerobic digesters produce biogas continuously and require a continuous process for desulfurisation. Commonly, H2S is removed using adsorption to solid media (iron sponge) or absorption and removal through chemical processes (scrubbing), requiring regeneration or replacement of sorbents. As an alternative, a continuous, anaerobic H2S removal process, utilising purple phototrophic bacteria was developed. The removal is driven by light as an energy source and potentially reduces the requirement for caustic. A desulfurisation bubble column was fed continuously with a synthetic biogas mixture (2000/5000 ppmV H2S, 30% CO2, CH4 balance) at sulfide loading rates ranging from 3.06 to 11.88 mg-S d−1. The liquid was inoculated with purple phototrophic bacteria, nutrients supplied via centrate, an anaerobic digestion residue, and externally irradiated with IR-light. The maximum sulfide removal rate was 10.13 ± 0.06 mg-S (Lh)−1 at a loading rate of 11.83 mg-S (Lh)−1, and the biomass oxidised the sulfide to sulfate utilising electrons for growth. Initially, caustic was dosed to control pH, which was replaced by hydraulic flushing (HRT 4 days), resulting in a mean pH of 6.8 at applied sulfide loading rate of 9.44 mg-S (Lh)−1. A reduction in HRT to 2 days resulted in performance loss. Thus, controlling the biomass inventory was found to be the major challenge of the process. Overall, the process can run caustic-free, and integrate with anaerobic digestion using the centrate as a nutrient source, with light supply limiting feasibility for night-time operation in a scaled process.

Effects of sponge iron dosage on nitrogen removal performance and microbial community structure in sequencing batch reactors

The application of sponge iron (SI) carriers can improve the biochemical treatment performance of sequencing batch reactors (SBR) during wastewater treatment. This study used SBR reactors to explore the effects of SI dosage on the nitrogen removal performance and reactor stability and microbial community structure under low temperature and ultra-low load. In contrast to conventional SBR, the average removal rate of total nitrogen (TN) in the biological sponge iron system (BSIS) was increased by 5.38 % for 45 g/L, 18.93 % for 90 g/L, and 13.52 % for 135 g/L, respectively. The nitrogen removal performance and reactor stability showed the best performance under the SI dosage of 90 g/L. The addition of SI formed the anaerobic-anoxic-aerobic microenvironments, which facilitate the propagation of denitrifying bacteria (Saccharimonadales, Hydrogenophaga) and iron bacteria (Rhodoferax and Acinetobacter) in the BSIS. This study provides a new insight on the application of SI in the wastewater treatment.

Synergistic improvement of nitrogen and phosphorus removal in constructed wetlands by the addition of solid iron substrates and ferrous irons

Sanjiang Plain is intensively used for rice production, and ditch drainage diffuse pollution prevention is crucial. Groundwater, rich in Fe ions, is the main source of irrigation water in this region. In this study, pyrite and zero-valent iron (ZVI) (sponge iron and iron scraps) were used as substrates to identify the synergistic influence of exogenous Fe2+addition and solid iron substrates on pollutant removal in constructed wetlands. Based on the results, iron substrates hardly improved the ammonia removal, mainly because of the physical structure and oxidation activity. At a hydraulic retention time longer than 8 h, the pollution removal efficiency in the zero-valent iron (ZVI) substrate treatment increased significantly, and the removal of nitrate (NO3−-N) and total phosphorus (TP) in the iron scrap substrate treatment reached about 60% and 70%, respectively. The high-throughput sequencing results showed a significant increase in the abundance of microorganisms involved in denitrification and phosphate accumulation in biofilms on ZVI substrates. The highest diversities of such microorganisms in biofilms on iron scraps were found for denitrifying bacteria (Pseudomonas), nitrate-reducing Fe (II)-oxidizing bacteria (Acidovorax), and Dechloromonas with autotrophic denitrification and phosphate accumulation, with a 43% cumulative abundance. Dechloromonas dominated in the iron sponge substrate treatment. The highest relative abundance of Acidovorax was found in the mixed iron substrate (pyrite, sponge iron, and iron scraps) treatment. The addition of ZVI substrate significantly improved the removal of NO3−-N and TP and reduced the hydraulic retention time through the continuous release of Fe2+ and the promotion of microbial growth. When designing constructed wetlands for treating paddy field drainage, the appropriate addition of iron scrap substrates is recommended to enhance the pollutant removal efficiency and shock load resistance of CWs.

An energy optimization study of the electric arc furnace from the steelmaking process with hot metal charging

A study of energy optimization derived from simulation software has been done for the high-intensity energy of an Electric Arc Furnace (EAF), hot metal charging within the cooler duct dedusting system. The present work aims to develop a dynamic model of the EAF operation based on mass and energy balances integrated with simulation of the dedusting system with hot metal charging system using MATLAB® and Computational Fluid Dynamics (CFD). The effect of various percentages of hot metal charging on EAF performance and the dedusting system was simulated and validated from the real EAF data plant from one of the steel manufacturer companies in Indonesia. Three cases for the EAF with various hot metal (HM), sponge iron, and scrap iron charging compositions and four cases for the EAF with post-combustion CO have been developed. Careful observation shows that the electric arc power consumption can be reduced down to 72.9 MWh from 87.4 MWh (ca. 16% more efficient) while at the same time increasing the HM charging temperature at the endpoint of the duct dedusting system up to 900°C from 540°C (app. 65% higher). Additionally, advanced simulation of an EAF with post-combustion CO shows that power consumption can be decreased to 59.9 MWh (ca. 30% more efficient).

Strengthen the purification of eutrophic water and improve the characteristics of sediment by functional ecological floating bed suspended calcium peroxide and sponge iron jointly

To overcome the shortcomings of conventional ecological floating bed (CEFB) in purifying landscape water, this study constructed a functional ecological floating bed (FEFB) through the suspension of calcium peroxide (CP) and sponge iron (SI) jointly below the CEFB. The purification effect of water quality and influence of sediment were compared in control check, CEFB, and FEFB systems, which were loaded the same sediment and reclaimed water in a field experiment. Results showed that the FEFB suspended with CP and SI had evident purification effect on the quality of landscape water supplied with reclaimed water and can maintain stably the nutrient status of the water body at mesotrophic levels and low turbidity. The FEFB promoted the degradation of humus, thus eliminating the chroma risk in water body caused by the decay of plants from the CEFB. Moreover, the FEFB can control the sediment mass produced, reduce the total nitrogen (TN) mass of sediment, and decrease the transformable TN (TTN) content in the sediment. The FEFB enhanced the stability of phosphorus (P) in the sediment, where the relative content of Ca–P and stable P reached 42.18% and 64.27%, respectively. To sum up, the FEFB suspended with SI and CP can not only effectively control the eutrophication and sensory index of landscape water but also change the TTN content and P forms in sediment, making the sediment more stable. Thus, the FEFB provides an innovative approach to reduce endogenous nutrient release for landscape water along with recharging with reclaimed water.

Simultaneous nitrate and phosphate removal based on thiosulfate-driven autotrophic denitrification biofilter filled with volcanic rock and sponge iron

This study constructed two thiosulfate-driven autotrophic denitrification biofilters filled with volcanic rock (VR-BF), sponge iron and volcanic rock (SIVR-BF), respectively. The nitrate removal load (3200 g/m3/d) and efficiency (98 %) of SIVR-BF were higher than those of VR-BF. The removal of phosphate in SIVR-BF was mainly through forming FePO4 and Fe3(PO4)2(OH)2. Sulfur and iron cycles in SIVR-BF contributed to Fe (II)/Fe (III) electron shuttle, as well as S2−, S0, Sn2− electron buffer and energy storage, which improved nitrate removal and electron utilization. The formation of multi-path collaborative denitrification dominated by sulfur autotrophic denitrification (64.2 ∼ 89.6 %) in SIVR-BF. The other denitrification pathways, such as iron autotrophic denitrification, which buffered pH and reduced sulfate production. Thiobacillus (38.6 %) and Ferritrophicum (25.3 %) were the dominant genus of VR-BF and SIVR-BF, respectively, which played crucial roles in autotrophic denitrification of iron and sulfur. SIVR-BF was a promising process to realize iron-sulfur coupling autotrophic denitrification and phosphate removal.

Catalytic activity and mechanism of typical iron-based catalysts for Fenton-like oxidation

Heterogeneous Fenton-like systems were exploited for the degradation of Reactive Red X–3B (RR X–3B) using iron-carbon composite, sponge iron, chalcopyrite and pyrite as catalysts. The effect of operational variables on the catalytic activity and metal leaching behavior of catalysts was evaluated and the catalytic mechanism was discussed. The experimental results showed that under the optimum conditions, chemical oxygen demand (COD) removals by Fenton-like systems could reach 89.91%, 86.84%, 80.11% and 60.02% with iron-carbon composite, sponge iron, chalcopyrite and pyrite, respectively. Micro-electrolysis of iron-carbon composite and sponge iron resulted in higher COD removal at acid pH range. Electron Paramagnetic Resonance (EPR) analysis and quenching tests showed that •OH was the main reactive oxygen species responsible for the degradation of RR X–3B. A large amount of Fe2+ leached from iron-carbon composite and sponge iron, which served as a homogeneous Fenton catalyst during the degradation of RR X–3B. In contrast, much lower amount of Fe2+ was leached from chalcopyrite and pyrite, and surface catalysis of the minerals played more important role in the generation of •OH. Surface characterization and density functional theory (DFT) calculation results illustrated that ≡Fe(II) was the primary surface catalytic site during the reaction. The reduction of ≡Fe(III) and ≡Cu(II) can be facilitated by sulfides on the mineral surface. The Fenton-like systems catalyzed by iron-based materials exhibited higher H2O2 utilization and COD removal than classical Fenton system. With the lower metal leaching concentration and stable surface property, chalcopyrite and pyrite may be more practical applicable from a long-term catalytic activity point of view.

Performance of hydrogel immobilized bioreactors combined with different iron ore wastes for denitrification and removal of copper and lead: Optimization and possible mechanism

Reasonable and efficient removal of mixed pollutants (nitrate and heavy metals) in industrial wastewater under heavy metal pollution has attracted more attention in recent years. The target strain Aquabacterium sp. XL4 was immobilized with different iron ore wastes (IOW) using polyvinyl alcohol (PVA) to construct four immobilized bioreactors. The results showed that when the ratio of C/N was 1.5 and the hydraulic retention time (HRT) was 8.0h, the denitrification performance of the bioreactor was the best, and the maximum denitrification efficiency of the bioreactor with sponge iron (SI) as the iron source was 97.19% (2.42mg L–1 h–1). Furthermore, by adjusting the concentration of Cu2+ and Pb2+, the stress behavior of the bioreactor to heavy metals under the influence of each IOW was investigated. The bioreactor has stronger tolerance and removal efficiency to Pb2+ and Cu2+ in the presence of pellets ore (PO) and refined iron ore (RO), respectively. Moreover, the high–throughput data showed that Aquabacterium accounted for a high proportion in the immobilized bioreactor, and the prediction of functional genes based on the KEGG database showed that the addition of IOW was closely related to the acceleration of nitrate transformation and the inflow and outflow of iron in cells.

Performances and enhanced mechanisms of nitrogen removal in a submerged membrane bioreactor coupled sponge iron system.

Sponge iron is a potential material for nitrogen removal, but lack of a study about nitrogen removal in a membrane bioreactor (MBR) coupled with sponge iron. The performances and mechanisms of nitrogen removal of SI-MBR were investigated and compared it with that in GAC-MBR. The results showed that the average rate of organic matter removal in the SI-MBR was 92.74%, which was higher than that in the GAC-MBR (87.48%). And the average effluent NO2--N and NO3--N concentration in the SI-MBR (0.02mg/L and 3.73mg/L) was lower than that in the GAC-MBR (0.05mg/L and 7.51mg/L). Meanwhile, the highest nitrification rate and denitrification rate was respectively 3.544±0.25 mg/(g VSS·h) and 6.643±0.2 mg/(g VSS·h) in the SI-MBR, which was higher than that (3.094±0.25 mg/(g VSS·h) and (6.376±0.2 mg/(g VSS·h)) in the GAC-MBR. Additionally, the bacterial activities (e.g., DHA activity and respiratory activity) were obviously enhanced through the iron ion from sponge iron. The bacterial community in the SI-MBR system was more richness and diverse than that in the GAC-MBR. Ultimately, the mechanisms of enhanced biological nitrogen removal with sponge iron in MBR were analyzed. On the surface of sponge iron, the DIRB and FOB could use the iron ion from sponge iron as the electron transfer to improve the nitrogen and organic removal. With sponge iron, there is not only the nitrification bacteria and heterotrophic denitrifying microorganism enriched, but also the autotrophic denitrifying bacteria abounded obviously. The autotrophic denitrifying bacteria could use Fe(II) as an electron donor to achieve denitrification and enhance the nitrogen removal.

Methane pyrolysis on sponge iron powder for sustainable hydrogen production

Methane pyrolysis is one of the possible methods to produce low-carbon hydrogen. One of the most promising catalysts for methane pyrolysis is Fe due to its availability, relatively low cost and high working temperature. In the presented paper, the methane pyrolysis on unsupported (without a carrier) sponge iron in the form of powder was studied in the temperature range of 700–1100 °C. Methane pyrolysis was carried out in a stainless-steel tube reactor with an inner diameter of 10 mm. The reactor was heated locally by propane burner, the length of the heated zone was about 8 cm along the reactor tube. Methane feed rates were about 50, 100, and 200 ml/min, and the residence time of methane in the 8 cm long reaction zone was about 4, 2 and 1 s, respectively. The hydrogen yield increased with an increase in the temperature and a decrease in methane feed rate. At 700–800 °C, the hydrogen yield did not exceed 20%. At 900 °C, the yield reached 28.6% at a residence time of about 4 s. At 1000 °C, hydrogen yield was about 40 and 66.5% at a residence time of about 1 and 4 s, respectively. At 1100 °C, hydrogen yield varied in the range of 70–85%. The use of a catalyst increased the hydrogen yield by 81% compared to the experiment without a catalyst at 1100 °C. The catalytic effect of sponge iron powder can be used in the development of methane pyrolysis plants.

Direct reduced iron and zinc recovery from electric arc furnace dust

AbstractBACKGROUNDAt present, the volumes of use of electric arc furnace (EAF) dust are extremely insignificant. The volumes of their formation amount to thousands of tons per month. During storage, they have a negative impact on the environment. At the same time they are a material that has a valuable composition (oxides of iron, non‐ferrous metals, etc.) and is promising for recycling. However, the secondary use of zinc‐containing EAF dust in ferrous metallurgy leads to the accumulation of zinc in the lining of blast furnaces and frequent malfunctions.RESULTSIt has been established that zinc oxide is mainly in the bound state in the composition of the franklinite phase (Zn,Mn,Fe)(Fe,Mn)2O4. The processes of solid‐phase reduction of EAF dust with the production of zinc concentrate and sponge iron, which are in demand as raw materials for non‐ferrous and ferrous metallurgy, have been studied. The optimal conditions for the reduction process were determined and the physicochemical characteristics, granulometric and phase composition of the initial materials, and reduction products were investigated.CONCLUSIONSIt has been established that the use of a combination of reducing agents of different nature (coal coke and H2) during heat treatment at 1100 °C and cooling in a reducing medium (Ar/H2, 5 vol%) makes it possible to obtain sponge iron with impurities (the highest degree of iron metallization was 97.5%), and zinc oxide with a basic substance content of about 98.4 wt.%. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Processing and physico‐mechanical characterization of sponge iron slag filled ramie fiber reinforced epoxy‐based composites

AbstractThe present research focuses on developing a new class of hybrid composites with woven ramie fiber mats reinforced in epoxy resin filled with different proportions of sponge iron (SI) slag. These multi‐layered composites are fabricated using conventional hand layup method. The cured composite samples are subjected to various physical, mechanical and micro‐structural characterization tests. Properties such as composite density, void content, tensile strength, flexural strength, impact and inter‐laminar shear strength, micro‐hardness, and so forth, are evaluated under controlled laboratory conditions. The compositional/micro‐structural features are identified with the help of scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), stereo‐microscopy, X‐ray diffraction, and so forth. Scanning electron microscopy reveals the shape, size and distribution pattern of the filler particles in the composites. The FTIR study is done to identify the functional groups present in the filler, fiber and in the resulting composite to get an insight to the chemistry of composite formation. Similarly, X‐Ray diffraction curve reveals the presence of hard phases such as silica, magnesioferrite, graphite, hematite, and so forth. This work suggests that successful fabrication of natural fiber composites is possible with additional reinforcement of an industrial waste like sponge iron slag and that most of the mechanical properties improve with increase in the content of SI slag in the composite.

Temperature Effects on PCE Degradation on ZVI in Column Experiments with Deionized Water.

The effects of rising groundwater temperatures on zerovalent iron (ZVI)-based remediation techniques will be critical in accelerating chlorinated hydrocarbon (CHC) degradation and side reactions. Therefore, tetrachloroethylene (PCE) degradation with three ZVIs widely used in permeable reactive barriers (Gotthart-Maier cast iron [GM], Peerless cast iron [PL], and ISPAT sponge iron [IS]) was evaluated at 10-70 °C in deionized water. From 10 to 70 °C, PCE degradation half-lives decreased from 25 ± 2 to 0.9 ± 0.1 h (PL), 24 ± 3 to 0.7 ± 0.1 h (GM), and 2.5 ± 0.01 to 0.3 ± 0.005 h (IS). Trichloroethylene (TCE) degradation half-lives at PL and GM decreased from 14.3 ± 3 to 0.2 ± 0.1 h (PL) and 7.6 ± 2 to 0.4 ± 0.1 h (GM). This acceleration of CHC degradation and the stronger shift toward reductive β-elimination reduced the concentration of potentially harmful metabolites with increasing temperatures. PCE and TCE degradation yields an activation energy of 28 (IS), 58 and 40 kJ mol-1 (GM), and 62 and 53 kJ mol-1 (PL). Hydrogen gas production by ZVI corrosion increased by 3 orders of magnitude from 10 to 70 °C, and an increased chance of gas clogging was observed at high temperatures.

Synthesis of Ag-Cu co-doping sponge iron-based trimetal for boosting simultaneous degradation of combined pollutants

To date, zero-valent iron (ZVI)-based technique has encountered a baffle, challenging simultaneous detoxification of refractory rhodamine B (RhB) and p-nitrophenol (PNP) possessing strong electronwithdrawing nitro-group. In this study, we synthesized Ag-Cu decorated sponge iron (s-Fe0)-based trimetal for simultaneous degradation of RhB and PNP. The results show that Cu-Ag co-doping s-Fe0 (s-Fe0-(Cu-Ag)) achieves approx. 90.6 % of maximized removal of RhB; the preferred s-Fe0-(5 wt%Cu-1 wt%Ag) assisted with 6 L/min aeration rate simultaneously declines RhB and PNP within 10 recycling tests; non-aeration process obtains a complete reduction of PNP as well as merely approx. 23.9 % removal of RhB. Moreover, the Cu-Ag microstructure covering s-Fe0-(Cu-Ag) has been characterized in detail. Furthermore, the electron spin resonance (ESR) spectra have been applied to investigate simultaneous generation of reactive oxygen species (ROSs) and hydrogen radicals ([H]abs) over s-Fe0-(Cu-Ag). To our best knowledge, this is the first study reporting the enhanced bifunctional catalysis of s-Fe0-(Cu-Ag)/O2 for simultaneous degradation of RhB and PNP.

Achieving deep autotrophic nitrogen removal in aerated biofilter driven by sponge iron: Performance and mechanism

Different from anammox, the combination of Fe (III) reduction coupled to anaerobic ammonium oxidation (Feammox) and nitrate/nitrite dependent ferrous oxidation (NDFO) do not require to control nitrite accumulation. Furthermore, sponge iron can avoid continuous iron supplementation in practice and is a good iron source for the occurrence of Feammox and NDFO in wastewater treatment. Therefore, a biofilter using sponge iron as carrier treating low nitrogen wastewater was built. In this study, the performances of nitrogen removal were explored under different hydraulic retention times (HRT) and gas-water ratios in sponge iron biofilter. And the pathways of nitrogen removal were analyzed by activity tests. The results showed ammonia removal efficiency reached 94.1% and total inorganic nitrogen removal efficiency was up to 70.6% at HRT of 19 h and gas-water ratio of 18. Compared to nitrogen removal by adsorption under non-aeration, the activity tests showed that total inorganic nitrogen loss was caused by Feammox and NDFO after aeration. The results of microbial communities showed that appearances of nitrifier-Nitrosomonadaceae, Feammox bacteria-Clostridiaceae and NDFO bacteria-Gallionellaceae resulted in deep nitrogen removal after aeration, in which Nitrosomonadaceae and Clostridiaceae contributed to ammonia removal and Gallionellaceae contributed to nitrite/nitrate reduction to nitrogen gas. Therefore, it was feasible to achieve deep autotrophic nitrogen removal and Fe (II) and Fe (III) cycle in sponge iron biofilter.

Separation of iron and zinc components dust of gas cleaning devices of the electric steelmaking productions

Currently, the volumes of use of dust from gas-cleaning devices (DGD) of electric steel furnaces are extremely insignificant, as they have an impact on the environment during storage, but at the same time, they represent the material that has a valuable composition (oxides of iron, non-ferrous metals, etc.) and is promising for recycling. However, the secondary use of zinc-containing DGD in ferrous metallurgy leads to the accumulation of zinc in the lining of blast furnaces and frequent malfunctions. It has been established that zinc oxide remains mainly in the bound state in the franklinite phase (Zn,Mn,Fe)(Fe,Mn)2O4. The processes of solid-phase reduction of dust from gas-cleaning devices of electric steel furnaces with the production of zinc concentrate and sponge iron, that are raw materials in demand for non-ferrous and ferrous metallurgy, are studied. The optimal conditions for the reduction process were determined, the physicochemical characteristics, granulometric and phase composition of the starting materials and reduction products were studied. It has been established, that the use of a combination of reducing agents of different nature (coal coke and H2) during heat treatment at 1100 °C and cooling in a reducing medium (Ar/H2) makes it possible to obtain sponge iron with a high degree of metallization - 97,5 %.

Effects of Recycled Sponge Iron on Phosphorus Recovery from Polluted Water

Phosphorus in water not only degrades water quality but also leads to a waste of resources. In this study, adsorption thermodynamics and kinetics were used to study the effect of sponge iron on phosphorus removal, and a filtration bed was used to simulate the phosphorus removal in polluted water. The results showed that the maximum theoretical adsorption capacity of the modified sponge iron was increased from 4.17 mg/g to 18.18 mg/g. After desorption with 18.18 mol/L of sodium hydroxide and reactivation with 6% (w%) sulfuric acid, the activation rate of modified sponge iron can reach 98%. In a continuous operation experiment run for approximately 200 days, the sponge iron phosphorus removal percolation bed showed a good phosphorus removal ability. Under the condition of TP = 10 mg/L, HRT = 1 H, the comprehensive phosphorus removal rate was 30–89%, and the accumulated phosphorus adsorption per unit volume was 6.95 kg/m3. Wastewater from the regeneration of the sponge iron base can be used to recover guano stone. The optimum conditions were pH = 10, n (Mg2+):n (PO43−):n (NH4+) = 1.3:1:1.1. Under the optimum conditions, the phosphorus recovery rate could reach 97.8%. The method provided in this study has theoretical and practical significance for the removal and recycling of phosphorus in polluted water.

Transforming a Carbon Rich Metallurgical Residue from a Sponge Iron Production into a Hydraulic Binder

This paper explores the possibility to convert a metallurgical residue from a sponge iron production (MR) with approximately 20 wt% amorphous carbon into a hydraulic binder. The challenge lies in developing an industrially-realistic, simple and robust process that exploits the characteristics of the residue, instead of trying to introduce the residue in an existing process. In the first stage the goal was to direct the chemistry of MR towards a “classical” ordinary Portland cement (OPC) clinker composition, while in the second stage the goal was to develop a process in which the carbon from the mixture would be used as a fuel to reach the desired temperature. Lab scale experiments have shown that the heat treated MR with 37 wt% CaCO3 contained, among others, all four cement clinker phases (i.e. C2S, C3S, C4AF and C3A). Upscaling experiments by means of sintering pan have further proven that such a material could be sintered in large quantities, while the energy from C burning was sufficient to achieve the required sintering temperature range (1000 – 1300 °C). The produced material consisted mainly of β-C2S, C3S, C4AF and C3A, and reached 28th day compressive strength of 28 MPa. This value is somehow lower than that of CEM I 32.5 N, yet the binder can be used in low- or non-load bearing applications.

Use of sponge iron as an indirect electron donor to provide ferrous iron for nitrate-dependent ferrous oxidation processes: Denitrification performance and mechanism

Sponge iron (SI) can serve as an indirect electron donor to provide Fe(II) for the nitrate-dependent ferrous oxidation (NDFO) process, producing OH– and magnetite. The SI–NDFO system mainly uses Fe(OH)2 as an electron donor, achieving a TN reduction rate of 0.42 mg–TN/(gVSS·h) for a period of at least 90 days. The enrichment of iron-oxidizing bacteria and the competition of iron-carbon micro-electrolysis for reaction sites on the surface of SI are the main reasons for the improvement of total nitrogen removal efficiency (TNRE). With an influent NO3––N concentration of 50 mg/L and a SI concentration of 50 g/L (at pH 5.0 and 30 °C), the TNRE reached a maximum level of 38.28%. In addition, reducing the pH environment was found to improve the denitrification efficiency of the SI–NDFO system, although denitrification stability was also reduced as a result. Overall, the SI-mediated NDFO process is a promising technique.