RESUMEN

Platinum group metals (PGMs) are strategic metals. Auto-exhaust catalysts are their main application fields. The recovery of PGMs from spent auto-exhaust catalysts has remarkable economic value and strategic significance. Aiming at the problems of ferrosilicon generation for Fe capturing and subsequent oxygen blowing to remove iron with high energy consumption and heat release, a technology of Fe-Sn synergistic capturing PGMs was proposed. Taking full the advantage of the lower melting point of Fe-Sn alloy (<1200 °C) and its unique affinity for PGMs, the PGMs were captured at approximate 1400 °C with Fe-Sn as the collector. In experiment, 500 g of spent auto-exhaust catalysts were employed to minimize error and approximate industrial production. The mechanism of Fe-Sn synergistic capturing PGMs was elucidated. The generation of Fe-Sn-PGMs alloy lowered the activity of [PGMs] in the system, accelerated the reduction of the PGMs oxides and promoted the alloying of [PGMs]. Therefore, Fe-Sn synergistic capturing PGMs was realized. The inability of Si to enter the alloy phase was confirmed by theoretical calculations, avoiding the generation of ferrosilicon. The effects of basicity, CaF2, m(Fe)/m(Sn) and the amount of collector on capturing PGMs were optimized. Under the optimized conditions (basicity R = 1.1, spent auto-exhaust catalysts 70 wt%, CaO 30 wt%, B2O3 10 wt%, CaF2 7 wt%, m(Fe)/m(Sn) = 1/1 and the collector 15 wt%), the content of PGMs in the slag phase was 2.46 g/t. It is feasible to remove Fe and Sn by oxidation to achieve the purpose of PGMs enrichment. This technology offers guidance on the safe, environmentally sound, and efficient disposal of spent auto-exhaust catalysts, promoting the sustainable development of PGMs.

Asunto(s)

Hierro , Platino (Metal) , Platino (Metal)/química , Hierro/química , Catálisis , Metales/química , Estaño/química , Aleaciones/química

RESUMEN

In this study, we present a bimetallic ion coexistence encapsulation strategy employing hexadecyl trimethyl ammonium bromide (CTAB) as a mediator to anchor cobalt-nickel (CoNi) bimetals in nitrogen-doped porous carbon cubic nanoboxes (CoNi@NC). The fully encapsulated and uniformly dispersed CoNi nanoparticles with the improved density of active sites help to accelerate the oxygen reduction reaction (ORR) kinetics and provide an efficient charge/mass transport environment. Zinc-air battery (ZAB) equipped CoNi@NC as cathode exhibits an open-circuit voltage of 1.45 V, a specific capacity of 870.0 mAh g-1, and a power density of 168.8 mW cm-2. Moreover, the two CoNi@NC-based ZABs in series display a stable discharge specific capacity of 783.0 mAh g-1, as well as a large peak power density of 387.9 mW cm-2. This work provides an effective way to tune the dispersion of nanoparticles to boost active sites in nitrogen-doped carbon structure, and enhance the ORR activity of bimetallic catalysts.

RESUMEN

We used magnesium slag (MS) as a calcium source for modifying coal gasification coarse slag (CGCS) in the presence of NaOH to prepare a novel phosphate adsorbent (MS-CGCS). Ca2SiO4 in MS reacts with NaOH during the high-temperature synthesis process, with sodium displacing a part of the calcium content in Ca2SiO4 and entering the mineral lattice to form Na2CaSiO4. Hydroxide ions reacted with calcium in Ca2SiO4 to generate Ca(OH)2 and decomposed into CaO at a high temperature. The two newly formed species participated in the phosphate removal. The MS-CGCS adsorbent showed good phosphate removal performance over a wide pH range, with a maximum phosphate adsorption capacity of 50.14 mg/g, which was significantly higher than that of other reported adsorbents. The Langmuir and pseudo-second-order models described the adsorption process well, indicating it being a monolayer and chemisorption process. The main mechanisms of phosphate removal are as follows: electrostatic interaction between the positively charged MS-CGCS and negatively charged phosphate ions; the inner-sphere complexation of oxides of metal, such as magnesium, aluminum, and calcium, with phosphate ions; and the precipitation of phosphate ions with calcium ions. Precipitation contributes to ~ 32% of the phosphate removal. This study provides a new method for the development of phosphate adsorbents while recycling CGCS and MS.

Asunto(s)

Fosfatos , Contaminantes Químicos del Agua , Fosfatos/química , Magnesio , Carbón Mineral , Calcio , Hidróxido de Sodio , Adsorción , Cinética , Concentración de Iones de Hidrógeno , Contaminantes Químicos del Agua/química

RESUMEN

Using fly ash as the main matrix for plant ecological restoration is effective for constructing a sustainable and ecological environment. The relevant properties of functional soil change due to different factors. Based on the orthogonal experiment of functional soil and the pot experiment of oat grass, fly ash was used as the matrix material for functional soil. Afterward, MX (large granules dispensing certain nutrients), SJJXWS (a water-retaining agent), and AF (a nutrient conditioner) additives were added to study the physical, chemical, and agronomic properties of functional soil, such as the emergence rate and weight of plants. The results showed the high pH and conductivity of functional soil, implying alkaline soils with high salinity. The contents of organic matter and available phosphorus and potassium were relatively high, indicating its high nutrient content. Further analysis revealed that the MX was the key factor affecting functional soil's electrical conductivity and evaporation, and thus, the corresponding plant emergence rate, plant weight, and other related indicators. The influence of each factor on the corresponding plant emergence rate, plant weight, and other indicators of functional soil was arranged in the order of MX (large granules dispensing certain nutrients), SJJXWS (a water-retaining agent), and AF (a nutrient conditioner). The optimum additive ratio in functional soil was 0.45 t·hm-2 of MX, 0.12 t·hm-2 of SJJXWS, and 1.65 t·hm-2 of AF. The results of this study provide a theoretical basis for further development of functional soil for ecological cycle restoration purposes.

RESUMEN

To better solve the waste pollution problem generated by the electrolytic manganese industry, electrolytic manganese slag as the main raw material, chromium iron slag, and pure chemical reagents containing heavy metal elements mixed with electrolytic manganese slag doping. A parent glass was formed by melting the slag mixture at 1,250°C, which was, thereafter, heat-treated at 900°C to obtain the glass-ceramic. The results from characterizations showed that the heavy metal elements in the glass-ceramic system were well solidified and isolated, with a leakage concentration at a relatively low level. After crystallization, the curing rates of harmful heavy metals all exceed 99.9%. The mechanisms of heavy metal migration, transformation, and solidification/isolation in glass-ceramic curing bodies were investigated by using characterization methods such as chemical elemental morphological analysis, transmission electron microscopy, and electron microprobe. The most toxic Cr and Mn elements were found to be mainly kept in their residual state in the glass-ceramic system. It was concluded that the curing mechanism of the heavy metals in a glass-ceramic can either be explained by the chemical curing induced by bonding (or interaction) during phase formation, or by physical encapsulation. Characterization by using both Transmission electron microscopy and EPMA confirmed that Cr and Mn were mainly present in the newly formed spinel phase, while the diopside phase contained a small amount of Mn. Zn, Cd, and Pb are not found to be concentrated and uniformly dispersed in the system, which is speculated to be physical coating and curing.

RESUMEN

In this work, a highly efficient wide-visible-light-driven photoanode, namely, nitrogen and sulfur co-doped tungsten trioxide (S-N-WO3), was synthesized using tungstic acid (H2WO4) as W source and ammonium sulfide ((NH4)2S), which functioned simultaneously as a sulfur source and as a nitrogen source for the co-doping of nitrogen and sulfur. The EDS and XPS results indicated that the controllable formation of either N-doped WO3 (N-WO3) or S-N-WO3 by changing the nW:n(NH4)2S ratio below or above 1:5. Both N and S contents increased when increasing the nW:n(NH4)2S ratio from 1:0 to 1:15 and thereafter decreased up to 1:25. The UV-visible diffuse reflectance spectra (DRS) of S-N-WO3 exhibited a significant redshift of the absorption edge with new shoulders appearing at 470-650 nm, which became more intense as the nW:n(NH4)2S ratio increased from 1:5 and then decreased up to 1:25, with the maximum at 1:15. The values of nW:n(NH4)2S ratio dependence is consistent with the cases of the S and N contents. This suggests that S and N co-doped into the WO3 lattice are responsible for the considerable redshift in the absorption edge, with a new shoulder appearing at 470-650 nm owing to the intrabandgap formation above the valence band (VB) edge and a dopant energy level below the conduction band (CB) of WO3. Therefore, benefiting from the S and N co-doping, the S-N-WO3 photoanode generated a photoanodic current under visible light irradiation below 580 nm due to the photoelectrochemical (PEC) water oxidation, compared with pure WO3 doing so below 470 nm.

RESUMEN

Zr-modified materials have an adsorption affinity for phosphate ions, but because of the cost of carrier materials, they are difficult to apply on a large scale. Herein, coal gasification coarse slag (CGCS) was used as a carrier material and modified with Zr, and its dephosphorization performance was studied. A series of adsorbents with different CGCS/ZrOCl2·8H2O mass ratios were prepared, from which the adsorbent with a CGCS/ZrOCl2·8H2O mass ratio of 5 : 4 (denoted as CGCS-Zr4) was identified as the most promising for phosphate adsorption. The specific surface area of CGCS-Zr4 was much greater than that of raw CGCS (100.12 vs. 12.43 m2 g-1). CGCS-Zr4 showed good adsorption selectivity towards phosphate when competitive anions co-existed, and exhibited good reusability; the adsorption capacity in the fourth adsorption-desorption cycle remained above 11.98 mg g-1. The adsorbent was also suitable for the continuous treatment of up to 830 and 743 bed volumes of synthesised and actual wastewater, respectively. The results of Fourier-transform infrared and X-ray photoelectron spectroscopy indicated that CGCS not only plays the role of a carrier, but also that Ca and Al in CGCS play an important role in phosphate adsorption. Compared with other carrier materials such as biochar and synthetic zeolite, CGCS has the advantages of a large stockpile, low cost, and easy availability. In addition, the preparation of CGCS-Zr4 is simpler and more energy-saving. Zr-modified CGCS is a promising dephosphorization material.

RESUMEN

A large number of natural aggregates are used in the field of construction materials, resulting in the exhaustion of natural aggregates. Therefore, looking for an alternative will slow down the consumption of natural aggregates. The sintering method not only consumes a lot of energy to prepare aggregates but also produces a lot of pollutants. In this study, silico-manganese (SM) slag was dried, ground into powder, and used as raw material. Solid and liquid alkaline activator methods were used to prepare SM slag non-burning aggregate (SMNA) by the cold bonding method. The effects of grinding time, amounts of solid and liquid alkaline activators, curing temperature, and the amount of added fly ash on aggregate properties were investigated. The aggregate microstructure was characterized by XRD, SEM, and FTIR methods, and the toxic leaching analysis of aggregate was performed. The results showed that with a fixed amount of liquid activator (16.2% wt.) and solid activator (15% wt.) and fly ash (20% wt.), respectively, and curing was performed at room temperature, the aggregate properties were optimal: the bulk density of 1236.6-1476.9 kg/m3 and the water absorption lower than 4.9-5.5%. The apparent density was 1973.1-2281.6 kg/m3, and the bulk crushing strength was 24.7-27.9 MPa. The XRD, SEM, and FTIR results indicated that amorphous gel could be formed from SM under an alkaline activator, improving the aggregate strength. The results of toxic leaching showed that the aggregate prepared from SM exhibited environmentally friendly characteristics. The SMNA was obtained via the simple and low-energy consumption production process, paving the new way toward large-scale utilization of SM.