Haiqing Hao

The similar surface physicochemical properties of ilmenite and forsterite make their selective flotation separation challenging. In this study, carboxymethyl sesbania gum (CMSG), a carboxymethylated derivative of sesbania gum (SG), was developed as a selective depressant for forsterite. At a CMSG dosage of 10 mg/L, single-mineral flotation tests achieved an 81.52% recovery difference between ilmenite and forsterite, 32.56% higher than that with SG. In artificial mixture flotation, CMSG maintained a comparable TiO2 recovery while increasing the TiO2 grade of the concentrate by 9.17% compared with SG. Multiscale characterization revealed that CMSG preferentially adsorbed onto the forsterite surface through chemisorption involving active Mg sites, forming a stable hydrophilic layer that reduced surface hydrophobicity and inhibited subsequent collector adsorption. In contrast, CMSG interacted with ilmenite primarily through weak physisorption, resulting in a limited effect on collector adsorption. Molecular dynamics simulations further revealed that the interaction energy of CMSG with ilmenite and forsterite reached -1568.31 and -4388.75 kJ/mol, respectively, confirming the substantially stronger interfacial interaction and more stable adsorption of CMSG on forsterite. This differential adsorption behavior enables selective depression of forsterite and efficient flotation separation of ilmenite, demonstrating the potential of structurally modified sesbania gum as a bio-based selective depressant.

Nanomaterials offer high specific surface area and tunable surface chemistry. They can be used as promising adsorbents, photocatalysts, and membrane components for wastewater treatment. However, problems of low efficiency and low recyclability limit the practical application of some nanomaterials. This review summarizes their use for inorganic and organic pollutant removal and examines defects. The modification and controllable construction of nanomaterials in terms of defect regulation, pore structure modification, and surface modification are also summarized. Pore and surface engineering strategies are discussed through a structure–property–performance framework. Then, improvements in pore and surface structures are investigated in relation to the controllable construction of nanomaterials. The evidence indicates that performance gains must be evaluated alongside regeneration, active-material leaching, transformation products, and energy demand. Future progress depends on reproducible comparisons, realistic wastewater testing, and recovery-by-design rather than removal efficiency alone.

The efficient beneficiation of low-grade Cu–Ni sulfide ores is challenging because Cu-bearing and Ni-bearing sulfide minerals are finely intergrown with gangue minerals. In this study, the ore composition and mineral liberation characteristics were examined, and different flotation flowsheets were evaluated. A flotation feed containing 80% of particles finer than 0.074 mm was selected by balancing mineral liberation against the adverse effects of excessive fines. After flowsheet optimization, a partially preferential flotation strategy was adopted, in which most Cu was first recovered into a Cu concentrate, and the remaining Cu was recovered together with Ni in a Cu–Ni bulk concentrate. For the closed-circuit flowsheet, an economic Cu concentrate with a Cu grade of 20.65% and Cu recovery of 78.77%, and qualified Cu–Ni bulk concentrates with a Ni grade of 5.43% and Ni recovery of 61.99%, were obtained. The comprehensive recovery rate of Cu was 88%. Partially preferential flotation simplifies the separation flowsheet of Cu–Ni ores while achieving substantial recovery of valuable metals. The technology is highly efficient and economical, and has broad application prospects for the beneficiation of low-grade Cu–Ni sulfide ores.

Low-grade and high-reserve scheelite, which is associated with calcite, has similar surface properties that cause difficulty in separation. In this study, sulfomethylated kraft lignin (SMKL) was used as a novel eco-friendly inhibitor for the flotation separation of scheelite and calcite. The flotation test results showed that 60 mg/L SMKL had a significant influence on depressing calcite flotation, while it had a slight effect on scheelite flotation. Furthermore, it enhanced the WO₃ grade of the concentrate in the artificial mixed ore to 62.02% with a recovery rate of 80.37%. The contact angle and zeta potential showed that SMKL could effectively decrease the surface floatability of calcite and caused the negative shift of minerals’ surface potential. XPS and DFT calculations revealed that the sulfonic acid group of SMKL had an electron-donating ability and was easily adsorbed on the positively charged surface of calcite, which hindered the adsorption of sodium oleate on calcite. SMKL could separate calcium-bearing minerals with a high efficiency and selectivity, providing a new method for industrial production.

Selective depressant plays an important role in mineral flotation. In this work, a low molecular weight carboxylated starch (LMWCS) was prepared as the selective depress ant for the separation of forsterite and ilmenite by flotation. Flotation behaviors and adsorption mechanisms were investigated using micro-flotation experiment, zeta potential, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and quartz crystal microbalance with dissipation (QCM-D). Compared to the conventional natural starch, the LMWCS has stronger depression on the flotation of forsterite. The XPS analysis proved that the LMWCS was adsorbed onto the Ti active site of ilmenite surface by weak hydrogen bond and onto the Al active site of the forsterite surface by strong chemisorption. The AFM and QCM-D analysis showed that the adsorption layer density of the LMWCS on the forsterite surface is higher than that of ilmenite. Therefore, the LMWCS is an effective and promising depressant for the forsterite flotation.

Collectors commonly have synergetic effects in ores flotation. In this work, a waste engine oil (WEO) was introduced as a collector to an ilmenite flotation system with sodium oleate (NaOL). The results show that the floatability of ilmenite was significantly improved by using WEO and NaOL as a combined collector. The recovery of ilmenite was enhanced from 71.26% (only NaOL) to 93.89% (WEO/NaOL combined collector) at the pH of 6.72. The optimum molar ratio of NaOL to WEO was about 2.08 to 1. The WEO and NaOL also have synergetic effects for the collection of ilmenite, because to obtain the ilmenite recovery of 53.96%, the dosage of 45 mg/L NaOL is equal to 38.56 mg/L WEO/NaOL combined collector (30 mg/L NaOL + 8.56 mg/L WEO). In other words, 15 mg/L of NaOL can be replaced by 8.56 mg/L of WEO. It is an effective way to reduce the dosage of the collector and reuse WEO. Therefore, it is a highly valuable and environmentally friendly approach for WEO reuse. WEO mainly consists of oxygen functional groups, aromatics, and long-chain hydrocarbons, especially for the RCONH₂ and RCOOH, thereby forming a strong interaction on the ilmenite surface. The adsorption mechanism of waste engine oil and sodium oleate on the ilmenite surface is mainly contributed by chemical adsorption. Therefore, WEO exhibits superior synergistic power with NaOL as a combined collector. Herein, this work provided an effective collector for ilmenite flotation and a feasible approach for reducing NaOL dosage and recycling WEO.