Ancient and recent gold mine activities led to soil and groundwater pollution with various metal and metalloids including arsenic in North-West Iran. Drinking and irrigation water wells have been sampled with arsenic levels between 110 and 200 μg/L. The aquifer chosen for testing ColFerroX particles was located close to a small village. The water table was ca. 6.5 meters below ground and the Darcy flow was ca. 0.2 m/day.
Sediment and groundwater from the site were used in column experiments to show the applicability of the Colferrox™ particles for groundwater remediation and arsenic immobilization. By injecting the Colferrox™ particles, the arsenic was strongly retarted, even though the testing flow velocity was much higher than the groundwater velocity and hence the contact-time for equilibrium was not reached. Thus, the potential efficacy of a Colferrox™ in situ barrier could be demonstrated.
A pilot application was carried out using one injection well. Despite the extreme cold weather, the colloidal particles remained stable as suspension and did not loose their properties. A total volume of ca. 28 m3 was injected into the well. Injection pressure remained below 1 bar throughout the injection. No iron oxide was found in the downstream monitoring well, which confirms that all ColFerroX particles precipitated successfully within the intended radius of 3 meters from the injection points.
The arsenic concentrations in the groundwater were monitored over a period of 210 days. Despite relatively high background groundwater flow no iron oxide was measured at downstream confirming formation of an stable in situ barrier. The desired 50% reduction of arsenic concentrations in both injection and downstream observation well was immediately reached and were maintained throughout the monitoring period.
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Dr. Sadjad Mohammadian
Sadjad.Mohammadian@ColFerroX.eu
Tel: +49 (0) 176 6191 6476
