Geochemistry of arsenic in the holocene aquifer; south-western Bangladesh

This paper is targeting to explore the geochemical partitioning of Arsenic, As in the solid-water interface of the contaminated Holocene deltaic aquifer of the South-western part of Bangladesh. Observed relatively high HCO3 and DOC in groundwater, GW may have significant role in leaching As from the brown clay and the grey sand in the sediment-water interface. Sequential extractions followed by spectroscopic investigation of the subsurface sediment reveal that Fe and Al minerals are the two principal adsorbent surfaces for As. Potential As source mineral iron-pyrite was detected with XRD and TEM image successfully captured the Fe2O3 contents in the clay sediments. Vivianite and siderite are the two minerals as suggested by the geochemical code PHREEQC that may control the GW Fe and As concentrations. Leaching of As from the upper clay layers and partial adsorption of that in the deeper sandy layers are the key transport mechanism. A parametric partition coefficient, Kd model (R2 = 0.69) was derived from the solid-water interface parameters like GW-pH and the two other Gaussianised independent variables particularly logarithm of oxalic acid extractable Fe and Al contents of the contaminated aquifers. Such promising Kd model can easily be incorporated into the solute transport code for assessing the vulnerability of aquifers.