Preparation and properties of the persulfate gel materials and application for the remediation of 2,4-dinitrotoluene contaminated groundwater

This study aims to develop persulfate new gel sustaining-release material (PGSR) and gelatin-gel sustaining-release material (G-PGSR) that can be injected into aquifers and slowly release S2O82− to groundwater. Compatibility and miscibility of colloidal silica gels and gelatin with S2O82− were tested. Morphologies of the as-prepared PGSR and G-PGSR were observed by scanning electron microscope (SEM) and Fourier transform infrared spectrometer (FT-IR). Release characteristics of PGSR containing variable persulfate concentrations (from 1.25 wt% to 5 wt%), silica sol (from 30 wt% to 40 wt%), and gelatin (from 0.5 wt% to 2.0 wt%) were monitored. Viscosities of PGSR solution increased from 5 to 112 cP with increasing silica sol from 30 wt% to 40 wt% during the first 10 min. Viscosities of PGSR solution in 40 wt% silica sol increased to 346 cP within the 30 min and rapidly increased to 8000 cP within the next 30 min followed by the gelation phase. Gelation rates of the PGSR solution increased with increased persulfate concentrations from 1.25 wt% to 5.0 wt%. The maximum release rates achieved at 5 h in G-PGSR were 1.98 mg of S2O82− per min similar to that in PGSR. The release persulfate concentrations in G-PGSR suggested that gelatin and colloidal silica were both compatible and miscible with S2O82−. Meanwhile, the PGSR exhibits a characteristic two-phase increase in viscosity with increased silica sol concentrations, persulfate concentrations, and gelatin concentrations. Compared with the persulfate only system, the degradation efficiency of 2,4-dinitrotoluene (2,4-DNT) was achieved 91.5 % within 3 h, while 78.6 % and 66.9 % degradation efficiency were shown in PGSR and G-PGSR, respectively. The PGSR and G-PGSR both could create persistent oxidation degradation of 2,4-DNT. Results suggested that colloidal silica and gelatin could be used to create PGSR and G-PGSR for persistent oxidation in groundwater remediation.