Natural Sources of Iron and Manganese in Groundwater of the Lower Kelantan Basin, North-eastern Coast of Peninsula Malaysia: Water Quality Assessment and an Adsorption-based Method for Remediation
Transition metals contamination in groundwater is often a consequence of effluent discharge from industrial activities but may also be the result of natural processes. In the former case contamination hazard can be mitigated at source by adopting improved protocols for waste disposal. For the situation where dissolved metals enter groundwater systems by mechanisms such as silicate rock weathering, an economic method of water treatment is required, because of the need for continuous
... Shallow groundwater resources in the lower Kelantan Basin show anomalously high concentrations of iron and manganese. In some cases, other transition metals and metalloids such as arsenic are also present at elevated levels. The basin is predominantly drained by the Kelantan, Semerak, Kemsin, and Pengkalan Datu rivers these fluvial systems flow towards the northwest before discharging into the South China Sea. The groundwater is acidic to alkaline (pH 5.14 to 8.75) and is dominated by Na-HCO3 hydrochemical facies. Coupled mineral stability and aqueous geochemical models are used to establish the source of iron and manganese in the groundwater. High concentrations of dissolved iron and manganese are related to Na-Cl groundwater types. Geochemical modeling of Fe2+/Fe3+ and S2-/SO42- redox pairs shows the state of redox disequilibrium in the groundwater. Redox conditions control mineral precipitation and dissolution of iron oxy-hydroxides, acid volatile sulphides and subordinate influence from pH fluctuations governs the stability of iron bearing carbonates. Speciation modelling results show the presences of ferric iron complexes and aqueous sulphides, despite supersaturation with respect to hematite, goethite, and pyrite. Dissolved manganese in the groundwater possibly originated from the dissolution of amorphous oxide-hydroxides and siderite, having substituted for iron as a minor impurity. The vadose-phreatic zone boundary in the shallow unconfined aquifers fluctuation in response to seasonal recharge patterns. This cyclic process induces a concomitant fluctuation in redox state, influencing the stability of redox sensitive phases. The shallow sediments of the Kelantan Basin host high concentrations of iron and manganese bearing minerals that are subject to reductive dissolution during recharge events. Additionally, meteoric recharge is characteristically acidic, destabilizing iron bearing carbonates phases such as siderite and ankerite. Naturally occurring metals contamination in potable groundwater supplies requires an economical method of remediation to avoid environmental and human health risks. Synthesized magnetic nano-particles created by a one-step method shows effective removal capacity of high iron and manganese concentrations in the groundwater samples at room temperature. The result of this work show that the primary sources of transition metals contamination in potable groundwater is a consequence of natural processes. It is proposed that the nano particulate adsorption method that has recently been developed will provide for an economical method of purification treatment.