The preparation of geopolymers from tailings rich in quartz typically requires activation to enhance final strength, though the underlying mechanism remains unclear. Quartz, as a common inert gangue mineral in tailings, was selected as the research subject. Quartz with varying reactivity was prepared through mechanical activation of different particle sizes and used for geopolymer synthesis, aiming to elucidate the strengthening mechanism of activated quartz on geopolymers. When the activation time was identical, quartz particles of different sizes exhibited the same soluble silicon content. However, due to the increased surface-active groups after activation, geopolymers derived from larger quartz particles (5–8 mm) achieved compressive strengths of 57.24–64.73 MPa, while those from smaller particles (0.08–0.12 mm) only reached 43.83–50.42 MPa. After activation, the main active groups on the quartz surface were the Q n (n = 1, 2, 3) structures containing non-bridging oxygens and silicon radicals. The Q 1 and Q 2 structures mainly provide soluble silicon in geopolymerization and have little effect on the strength of the geopolymer. While the Q 3 structure can combine with the geopolymer gel through Si-O-Si bonds, reducing the porosity at the interface between quartz and geopolymer, significantly enhancing the strength of geopolymer. The results indicate that, compared to soluble silicon content of quartz, the content of active groups on its surface is the main factor influencing the performance of geopolymer. For the activation of tailings, increasing the reactivity of their surface is more effective in improving geopolymer strength than enhancing the leaching of soluble silicon and aluminum through overall activation.
Tong Chang,Renhui Deng,Jiaxin Xie,Jianyu Tang,Wenyao Gu,Zimin Peng,Suyao Liu
The abundant Si-OH groups serving as the defect sites in the ZSM-22 zeolite framework are not only closely associated with physicochemical properties and catalytic performance but are also the primary sites for attack by water molecules, thereby restricting applications involving or producing water. In the present study, a liquid-mediated healing process was used to convert the Si-OH groups in ZSM-22 zeolite into Si-O-Si bonds. The systematic investigation of the treatment solution’s composition and the hydrothermal conditions revealed that the crystallinity of ZSM-22 zeolite can be effectively enhanced following optimal healing treatment. Furthermore, the healed ZSM-22 zeolite exhibited enhanced ordering degree and pore connectivity without significant changes to the Si/Al and morphology. Moreover, the decline in Si-OH groups reduced the Lewis acid sites without altering the Brønsted acidity, which led to a slight decrease in the dispersion of Pt particles. In n-decane hydroisomerization, compared to the parent ZSM-22 zeolite catalyst, the healed catalyst demonstrates higher reactant conversion and increased isomer yield, attributing to its enhanced confinement within the micropore voids, which leads to a reduced yield of multi-branched isomers susceptible to cracking. This study presents a potential application of ZSM-22 zeolite in hydroisomerization for complex and challenging feedstocks.
This work focused on the construction of an acid-resistant composite nanofiltration membrane with the selective layer of bulk cross-linked hydroxyethyl cellulose (HEC)-silica and a support of porous polypropylene . Membranes were fabricated through in-situ sol-gel reaction and slot-die coating method employing tetraethyl orthosilicate (TEOS) as the silica precursor and cross-linking agent of HEC. Membrane structure and performance were tuned by controlling the hydrolysis time of TEOS and differentiating TEOS and HEC contents, and systematically characterized in terms of physico-chemical property, permeation attribution and acid stability. It was found that membrane performance was strongly correlated with the relative contents of C–O–Si and Si–O–Si bonds of the formed HEC-silica selective layer. High content of C–O–Si bond formed via condensation reaction of HEC and TEOS endowed the selective layer with denser network structure and good rejection ability. Both insufficient and excessive hydrolysis led to a poor rejection ability of formed membrane. The optimized HEC-silica membrane possessed an average pore size of about 1.43 nm within the scope of nanofiltration membrane, a high pure water permeability coefficient of around 10.5 LMH/bar, and a medium rejection of 85.2% to 500 mg/l Na 2 SO 4 aqueous solution at 5.0 bar. No changes in both chemical structure and separation performance occurred with the HEC-silica composite membrane after being soaked in aqueous H 2 SO 4 solution of 4.9 wt% for 7 days, while evident structure destruction and serious performance degradation occurred with the compared polyamide-based commercial membrane NF270. Long-term soaking test using 15.0 wt% H 2 SO 4 aqueous solution for 30 days also demonstrated that the acid resistance HEC silica membrane was comparable with those reported acid stable nanofiltration membranes. Furthermore, the HEC-silica membrane also maintained its water permeation and solute rejection abilities during a 30-day continuous filtration of aqueous solution of 4.9 wt% H 2 SO 4 and 50 mg/l polyethylene glycol fraction (PEG2000). The good acid resistance of the HEC-silica composite membrane was attributed to its bulk cross-linked network structure composed of C–O–Si, Si–O–Si and C–C bonds.
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