Xiangpeng Gao

This study delves into the exploration of gellan gum (GG) as a novel depressant to selectively separate specularite from chlorite through flotation processes. The single mineral flotation assessments unveiled that the introduction of GG notably inhibited the flotation of specularite, while exerting a comparably weaker effect on chlorite, in conjunction with dodecylamine (DDA) as the collector. GG significantly amplified the difference in floatability between specularite and chlorite in artificial mixed ore flotation. The adsorption mechanism revealed the selective adherence of GG to the surface of specularite, and that GG chemically bonded to the surface of specularite through a reaction between active groups (–COOH, –OH) in GG molecules and Fe sites on the specularite surface, forming Fe-O bonds. The application of GG emerges as a promising and effective depressant for the separation of specularite from chlorite, offering significant potential within this domain of study.

Aqueous phase of bio-oil (APB) is a general stream of waste produced from biomass pyrolysis and fractional condensation of pyrolytic volatiles and has very limited applications. We have demonstrated a sequence of leaching of alkali and alkaline earth metallic species (AAEMs) from char and catalytic hydrothermal gasification (CHTG) for valorizing char and APB, respectively. The majority of AAEMs can be removed from the char by leaching with APB and the removal rates were almost equivalent to those leached with HCl (1.0 M). CHTG of an aqueous solution of the spent APB with a total organic carbon of 14,450 ppm was performed in a continuous flow reactor, employing an activated carbon-supported Ru catalyst (Ru loading, 4.6 wt%). The catalyst exhibited a stable activity for carbon conversion of 98.8 % at 350 °C for at least 360 min while gaseous product consisting of H2, CH4, and CO2 was produced with a cold gas efficiency of 101–103 %, on a higher heating value basis. The cold gas efficiency exceeding 100 % is mainly because of the generation of H2 from water through water-gas shift reaction. The CHTG performance of APB was enhanced by char leaching through the uptake of coke-forming precursors of APB onto char and the enrichment of AAEMs in the spent APB. These AAEMs played roles in suppressing coke formation and deposition onto the catalyst and maintaining Ru particle size by providing a less acidic hydrothermal environment.

The surge in economic growth has spurred the expansion of the textile industry, resulting in a continuous rise in the discharge of printing and dyeing wastewater. In contrast, the photocatalytic method harnesses light energy to degrade pollutants, boasting low energy consumption and high efficiency. Nevertheless, traditional photocatalysts suffer from limited light responsiveness, inadequate adsorption capabilities, susceptibility to agglomeration, and hydrophilicity, thereby curtailing their practical utility. Consequently, integrating appropriate carriers with traditional photocatalysts becomes imperative. The combination of chitosan and semiconductor materials stands out by reducing band gap energy, augmenting reactive sites, mitigating carrier recombination, bolstering structural stability, and notably advancing the photocatalytic degradation of printing and dyeing wastewater. This study embarks on an exploration by initially elucidating the technical principles, merits, and demerits of prevailing printing and dyeing wastewater treatment methodologies, with a focal emphasis on the photocatalytic approach. It delineates the constraints encountered by traditional photocatalysts in practical scenarios. Subsequently, it comprehensively encapsulates the research advancements and elucidates the reaction mechanisms underlying chitosan based composite materials employed in treating printing and dyeing wastewater. Finally, this work casts a forward-looking perspective on the future research trajectory of chitosan based photocatalysts, particularly in the realm of industrial applications.

This contribution reports the effects of product recovery methods on the yields and properties of hydrochars produced from hydrothermal carbonization (HTC) of algal biomass. A slurry of Chlorella vulgaris with 10 wt% of solid loading was hydrothermally carbonized at 180 – 220 °C with holding time of 15 and 60 min. The resulting hydrochars were recovered by two prevailing methods, namely direct filtration and dichloromethane (DCM)-aided filtration. The results indicate that, under identical HTC conditions, compared with DCM-aided filtration, direct filtration always results in higher hydrochar yield because of the biocrude retained on its surface. The presence of residue biocrude in the hydrochars from direct filtration further leads to considerable differences in their properties, as compared with their counterparts from DCM-aided filtration. Specifically, under identical HTC temperature and holding time, DCM-aided filtration yields hydrochars of lower volatile matter contents but higher fixed carbon and ash contents, as compared with the hydrochars from direct filtration. Direct filtration generally recovers hydrochars of greater higher heating values and energy-based yields as compared to DCM-aided filtration. The product recovery methods show considerable impacts on the concentrations of Na, K, Mg, and Ca and their retentions in the hydrochars at 220 °C for 60 min, with higher concentrations and retentions of these elements being observed in the hydrochars from DCM-aided filtration. The hydrochars at 220 °C for 15 and 60 min from DCM-aided filtration show higher specific reactivity of 0.040 – 0.058 min−1 and 0.066 – 0.096 min−1 at hydrochar conversions of ≤ 82 % and ≤ 78 %, respectively, as compared with their direct-filtration counterparts, due to their higher concentrations of catalytic alkali and alkaline earth metals. These findings highlight the importance of considering product recovery methods when comparing the yields and properties of hydrochars from HTC of algae reported in the literature.

Photocatalysis has been widely used for the removal of hexavalent chromium from wastewater as an efficient and environmental friendly method. However, conventional photocatalysts generally exhibit poor adsorption properties toward Cr(VI), resulting in unsatisfactory performance in high concentrated wastewaters. In this study, we synthesized a novel composite material with high Cr(VI) adsorption ability by blending prepared CuS nanocrystals into triethylenetetramine modified sodium alginate for the enhanced photocatalytic removal of Cr(VI). Effect of CuS dosage, pH value, light source and intensity were discussed for the optimum Cr(VI) removal conditions. The synthesized composite has shown good adsorption performance toward Cr(VI) and the overall removal rate reached 98.99 % within 50 min under UV light irradiation with citric acid as hole scavenger. Adsorption isotherm, thermodynamics, and kinetics with corresponding model fitting were discussed, which suggested that the monolayer and chemical adsorption dominated the adsorption process. Characterization results indicated that amino and hydroxyl groups contributed electrons in the photocatalysis reaction for the reduction of Cr(VI) to Cr(III). CuS nanocrystals can enhance the surface charge and light absorbance ability of the composite, and the Cr(VI) removal was governed by electrostatic interaction and photo-induced redox reaction.

In this study, hydroxypropyltrimethyl ammonium chloride chitosan (HACC) was first introduced as a depressant during separating chalcopyrite from molybdenite (Cu-Mo). The selective effects of HACC on the separation of Cu-Mo were conducted by single-mineral flotation tests. The findings revealed that HACC helps separate Cu and Mo efficiently at pH 6 with 8 mg/L of HACC, resulting in 76.22% and 5.38% of Mo and Cu recovery, respectively. The adsorption mechanism of HACC was investigated via Zeta potential, adsorption density, contact angle, FT-IR and XPS analysis. The contact angle and adsorption density measurements offer indisputable proof that HACC can adsorb on the surface of chalcopyrite. Furthermore, FT-IR and XPS measurements confirm that N atoms in quaternary ammonium groups of HACC interact with Cu sites on the surface of chalcopyrite. The findings also suggest that HACC adsorbs on the surface without significantly impacting molybdenite. All these results confirm that HACC can be an effective chalcopyrite depressant.

To solve the problem that the iron-bearing silicate gangue aegirite is difficult to separate because of its own density, specific magnetization coefficient and mineral surface properties similar to those of iron oxide. The effect of thiosalicylic acid（TSA） on the floatability of specularite and aegirite under the condition of sodium oleate（NaOL） as collector was investigated by flotation test, and the depression mechanism of TSA on aegirite was studied by infrared spectroscopy（FTIR）, adsorption tests, Zeta potential detection, XPS analyses and Boltzmann theory analysis. The results show that TSA has a significant depression effect on aegirite and almost no depression effect on specularite. TSA mainly adsorbes on the surface of aegirite, resulting in a leftward shift of the iso-electric point of aegirite from 3.3 to 1.0, while it adsorbes less on the surface of specularite and its iso-electric point changes weakly. The -SH group in TSA combines with metal ions on the surface of aegirite to form metal complexes during the adsorption process, and the hydrophilic group -COOH increases the hydrophilicity of aegirite, which widenes the hydrophilic difference between aegirite and specularite, and achieves the selective depression effect on aegirite.

In this work, zeolite based on coal fly ash was firstly synthesized via wet milling for the adsorption of lead (Pb(II)). The effects of contact time, solid-to-liquid ratio and initial pH of solution on Pb(II) removal were investigated in detail. The experimental data showed that synthesized zeolite has high adsorption capacity of 99.082 mg of Pb(II) per gram of adsorbent. Coal fly ash zeolite synthesized by wet milling has good Pb(II) adsorption performance when the initial pH of the solution is above 5. The adsorption kinetic results demonstrated that removal of Pb(II) via the synthesized zeolite followed pseudo-second-order kinetic model. X-ray photoelectron spectroscopy results directly demonstrated the adsorption between Pb(II) and synthesized zeolite, and a possible reaction pathway was proposed. Specifically, the removing mechanism of Pb(II) from aqueous solution via the synthesized zeolite involves two stages: one is that Pb(II) in aqueous solution is absorbed on the interior of the synthesized zeolite, and the other is chemical precipitation.

Biomass utilization coupled with CO2 fixation offers a promising approach to produce sustainable carbon–neutral biofuels and chemicals while contributing to reducing CO2 emissions. In this study, we proposed a method for synchronous bio-oil upgrading and CO2 fixation by co-electrolysis in a sealed, undivided cell equipped with a metal cathode and a sacrificial anode. Results showed that the reactive components in bio-oil reacted with CO2 during co-electrolysis, enhancing the abundance of the esters and formic acid by 57.2% and 270.2%, respectively. The CO2 fixation rate was enhanced by 4.6% after co-electrolysis of bio-oil and CO2, with the control experiment in the absence of bio-oil. Additionally, the Cu cathode showed superior catalytic activation for upgrading bio-oil and achieving the highest CO2 fixation, owing to its high selectivity for multi-electro transfer products. To summarize, the ketones and the phenolic derivatives in bio-oil could react with CO2 to form organic esters and acids, while the 2–3 rings and heavy components in bio-oil tended to polymerize and generate insoluble products (polymers). Ultimately, we proposed a carbon-negative distributed biomass processing station system and discussed the future perspective on synchronous bio-oil upgrading and CO2 fixation by co-electrolysis in this work.

Pyrolysis of sewage sludge under conditions relevant to applied smouldering combustion was carried out in this study to investigate the influences of gas flow rate, oxidative atmosphere, and inert porous medium involvement on the properties of products. The experiments were carried out at 300–600 °C under atmospheres of N2, 5% O2/95% N2, 10% O2/90% N2, and 15% O2/85% N2, with Darcy flow rates of 1.0 and 3.5 cm/s, respectively, with dried sewage sludge loaded individually or as a mixture with sand. As a result, both the increment of gas flow rate and involvement of sand leaded to lower yields of char and higher yields of bio-oil and gas under N2 at temperature of ≤500 °C, due to the enhanced efficiency of pyrolysis reaction and gas transportation. However, when temperature increased to 600 °C, the influencing trends on product distributions changed due to the mechanisms of secondary cracking reaction and volatile-char interaction. The involvement of oxygen in fraction of ≤15 vol% at temperatures of 400–500 °C would lead to the intense decreasing yields of char and bio-oil, and increasing yield of the gaseous (dominated by CO2 and CO), due to the involved oxidation reaction during pyrolysis. Both increment of temperature and oxygen fraction would lead to the delay of ignition and the increase of activation energy of the produced char, except for that of char produced at 400 °C under 5% O2/95% N2, whose calculated activation energy was lower and volatile content was higher compared to that of char produced from pyrolysis at 400 °C under N2. The bio-oil from pyrolysis under N2 was dominated by aliphatic acids, phenols, steroids, amides, and indoles, etc., and the involvement of partial oxidation would lead to the weakened formation of aromatics, phenols, and S/Cl/F-containing compounds in bio-oil.