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High-fluorine groundwater is a potential threat to ecological environment and human health. The source and distribution of fluoride in groundwater in urbanized areas are complicated due to the double influence of geological background and human activities. It is of great significance to identify the characteristics of fluorine in groundwater to ensure the safety of groundwater.This study analyzed the environmental characteristics and main hydrogeochemical processes of high-fluorine groundwater in different urban functional areas of Lanzhou city, the largest industrial city in the arid region of Northwest China, based on the mathematical statistics, ion ratios and saturation index analysis. Then the influence of human activities on the migration and enrichment of fluoride was revealed. The results show that the ρ(F−) in the groundwater in the study area ranges from 0 to 4.8 mg/L, and 13 high-fluoride water samples exceeded the standard of groundwater quality Class III (1.0 mg/L), with an excess rate of 20.3%. Under the influence of intensity of human activity and sources of human input, the distribution characteristics of fluorine in groundwater in different urban functional areas are prominently different. The fluorine content of groundwater in the Xigu Petrochemical Industrial Zone is the highest, with the 47.4% of high-fluorine groundwater. While in commercial residential areas and new urban areas the fluorine content is relatively low, with the 7.1% and 9.7% of high-fluorine groundwater, respectively. The high-fluorine groundwater in the study area is mainly SO4•Cl—Na and Cl•SO4—Na type water, which is low in calcium, rich in sodium and weak in alkalinity. The dissolution of fluorinated minerals, precipitation/dissolution of calcite and dolomite, cation exchange between calcium and sodium on the surface of clay minerals, strong evaporation and salt effect are the main hydrogeochemical processes of fluoride enrichment in groundwater in the study area. Urbanization and industrialization lead to the further deterioration of natural high fluorine water, the industrial wastewater leakage from petrochemical leads to the further dissolution of fluoride in the formation, which is an important driving force for the enrichment of high fluorine groundwater in the Xigu Industrial Zone. The study provides basic information for the fluoride migration and enrichment in the high fluoride background area with human activities.

A hydrothermal alkali modification method was used to produce geopolymer (BFA-GP) from biofuel ash (BFA). The product was characterized by scanning electron microscopy with energy dispersive spectrometry (SEM-EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared reflection (FTIR), and X-ray photoelectron spectroscopy (XPS). Significant amount of geopolymer and gismondine was produced by this modification. The surface area increased from 20.41 m2 g−1 to 56.63 m2 g−1. The adsorption capacity of BFA-GP can reach 29.92 and 137.49 mg g−1 for Cd2+ and Pb2+, respectively, in a pure solution at 298 K, which is about triple of that by the original BFA. Competitive adsorption of Cd2+ and Pb2+ showed that the binding affinity is Pb2+> Cd2+. Chemical sorption including electrostatic attraction, chelate reaction, and ion-exchange is the dominant mechanism of heavy metal adsorption on BFA-GP. And the adsorption thermodynamics indicates that adsorption reaction of heavy metal ions by BFA-GP is spontaneous and endothermic. This modification provided a cost-effective and environmentally friendly way to change BFA to adsorbent for heavy metals with promising application prospects.