Saeedreza Hafeznezami (California) has published a research article entitled “Arsenic mobilization in an oxidizing alkaline groundwater: Experimental studies, comparison and optimization of geochemical modeling parameters” in Applied Geochemistry, the Journal of the International Association of GeoChemistry, on July 22, 2016.

Contamination of groundwater resources with naturally occurring arsenic (As) is a major health concern globally. Geochemical modeling can be a useful tool in predicting the mobility of As and assessing the remediation solutions for affected areas. Application of currently available surface complexation modeling (SCM) approaches for describing the adsorption of As on pure minerals has shown promising results. However, there is a need to further optimize the development and implementation of such mechanistic models for adsorption of solutes on natural heterogeneous solid phases.
This work compares and evaluates different methodologies to model dissolved As and phosphate concentrations from a series of batch experiments conducted on natural sediment and groundwater samples from a contaminated site in New England, USA. The easily-accessible modeling tools PHREEQC and FITEQL were utilized to predict and simulate the experimental results.

The SCMs developed in this study vary in terms of:

1. method for estimating the total number of sorption sites
2. method for describing the surface site heterogeneity
3. method for applying electrostatic and pH-dependent correction factors to surface reaction constants

Abstract

Arsenic (As) mobilization and contamination of groundwater affects millions of people worldwide. Progress in developing effective in-situ remediation schemes requires the incorporation of data from laboratory experiments and field samples into calibrated geochemical models.
In an oxidizing aquifer where leaching of high pH industrial waste from unlined surface impoundments led to mobilization of naturally occurring As up to 2 mg L−1, sequential extractions of solid phase As well as, batch sediment microcosm experiments were conducted to understand As partitioning and solid-phase sorptive and buffering capacity. These data were combined with field data to create a series of geochemical models of the system with modeling programs PHREEQC and FITEQL. Different surface complexation modeling approaches, including component additivity (CA), generalized composite (GC), and a hybrid method were developed, compared and fitted to data from batch acidification experiments to simulate potential remediation scenarios. Several parameters strongly influence the concentration of dissolved As including pH, presence of competing ions (particularly phosphate) and the number of available sorption sites on the aquifer solids. Lowering the pH of groundwater to 7 was found to have a variable, but limited impact (<63%) on decreasing the concentration of dissolved As. The models indicate that in addition to lowering pH, decreasing the concentration of dissolved phosphate and/or increasing the number of available sorption sites could significantly decrease the As solubility to levels below 10 μg L−1. The hybrid and GC modeling results fit the experimental data well (NRMSE<10%) with reasonable effort and can be implemented in further studies for validation.

More Information

For more information, or to read the article, visit: Applied Geochemistry

For information about The International Association of GeoChemistry (IAGC), visit: http://www.iagc-society.org

For more information on geochemical modeling parameters, contact Saeedreza Hafeznezami at SHafeznezami@Geosyntec.com.