High-Arsenic Groundwater from Huaihe River Basin, China：Geochemistry and Hydrogeochemical Processes

Arsenic (As) poses a danger to environmental health, and drinking arsenic-rich groundwater is a key exposure risk for humans. The distribution, migration, and enrichment of As in groundwater is an important worldwide environmental and public health problem that requires research. Huaihe River Basin has been newly identified as a region of high-arsenic groundwater in China. This study aims to analyze the hydrogeochemical data of high-arsenic groundwater, trace its formation and evolution, and evaluate its potential pollution risks. The results showed that As and F were the main inorganic chemical substances affecting the water quality in the study area, with concentrations of 5.75±5.42 μg L-1 and 1.29±0.40 mg L-1, respectively, exceeding the recommended drinking water standards of the World Health Organization by 23% and 31%, respectively. The proportion of groundwater with a high As content presents a high exposure risk. According to the hydrochemical diagram and the calculation of mineral saturation indices, the groundwater in the study area underwent evaporation, halite dissolution, and water-rock interaction. The total alkalinity of high-arsenic groundwater ranges mainly between 400–700 mg L-1, and the chemical type is mainly of HCO3-Na. High-arsenic groundwater is largely affected by evaporation and cation exchange. In an alkaline environment, As in high-arsenic groundwater derives from the dissolution and release of arsenic sulfide in aquifer sediments and poses a potential threat to human health through food and drinking water.

High-Arsenic Groundwater in Paleochannels of the Lower Yellow River, China: Distribution and Genesis Mechanisms

High–arsenic (As) groundwater poses a serious threat to human health. The upper and middle reaches of the Yellow River are well–known areas for the enrichment of high–arsenic groundwater. However, little is known about the distribution characteristics and formation mechanism of high-As groundwater in the lower reach of the Yellow River. There were 203 groundwater samples collected in different groundwater systems of the lower Yellow River for the exploration of its hydrogeochemical characteristics. Results showed that more than 20% of the samples have arsenic concentrations exceeding 10 μg/L. The high-As groundwater was mainly distributed in Late Pleistocene–Holocene aquifers, and the As concentrations in the paleochannels systems (C2 and C4) were significantly higher than that of the paleointerfluve system (C3) and modern Yellow River affected system (C5). The high-As groundwater is characterized by high Fe2+ and NH4+ and low Eh and NO3−, indicating that reductive dissolution of the As–bearing iron oxides is probably the main cause of As release. The arsenic concentrations strikingly showed an increasing tendency as the HCO3− proportion increases, suggesting that HCO3− competitive adsorption may facilitate As mobilization, too. In addition, a Gibbs diagram showed that the evaporation of groundwater could be another significant hydrogeochemical processes, except for the water–rock interaction in the study area. Different sources of aquifer medium and sedimentary structure may be the main reasons for the significant zonation of the As spatial distribution in the lower Yellow River.

An Electrochemical Process Comparison of As(III) in Simulated Groundwater at Low Voltage in Mixed and Divided Electrolytic Cells

A relatively low voltage can be favor of e- transfer and peroxide generation from dominant 2e--reduction of O2 on carbon materials as cathode, with low energy loss. In this study the conversion of As(III) in simulated high arsenic groundwater at low voltage was compared in a mixed and a anode–cathode separated electrolytic system. With applied voltages (the potential difference between cathode and anode) from 0.1 V to 0.8 V, As(III) was found to be efficiently converted to As(V) in the mixed electrolytic cells and in separated anodic cells. The complete oxidation of As(III) to As(V) at 0.1–0.8 V was also achieved on graphite in divided cathodic cells which could be long-running. The As(III) conversion process in mixed electrolytic cells, anodic cells and cathodic cells all conformed to the pseudo first-order kinetics equation. The energy consumed by As(III) conversion was decreased as the applied voltage declined. Low voltage electrolysis is of great significance for saving energy consumption and improving the current efficiency and can be applied to in-situ electrochemical pre-oxidation for As(III) in high arsenic groundwater.