Theme: 08. Metals

Topic Area: 8a. Managing Chromium-Contaminated Sites

Formatted Title:

Pilot Test with Combined Electrokinetic Remediation and Pumping Techniques for a Metal-Impacted Area

Background/Objectives:

The study area is an industry that manufactures chemical products for water treatment located in São Paulo, Brazil, and exhibits contamination of aluminum, barium, lead, cobalt, copper, chromium, iron, manganese, molybdenum, vanadium, nickel, and zinc in an aquifer composed of altered silt soils. The highest concentrations are observed for iron and aluminum, with concentrations of up to 3.6 g/L and 2.7 g/L, respectively. Furthermore, the groundwater pH in some wells located near the center of mass is extremely low, less than 2, resulting in conditions favorable for increased metal mobilization due to the acidity of the water. Due to the presence of water bodies near the industry and mathematical modeling indicating the contribution to the water bodies even after 20 years, it was decided to conduct a pilot test combining electrokinetic remediation with pumping to assess the potential applicability of these techniques in combination for the remediation of the area.

Approach/Activities:

The pilot test involved the installation of two wells for electrode insertion and pumping with a 5.0-m spacing between them, as well as the installation of observation wells at various distances from the wells containing the electrodes. The test lasted for 14 days, during which samples were collected from the observation wells before and after the test, sampling of the pumped effluent during the operation, and the precipitated material at the end of the test for chemical analysis of metals. Through the graphite electrodes installed in each well, an average voltage of 24 V was applied, and pumping was carried out using automatic peristaltic pumps installed in each well with a flow rate of 6 L/h per well due to the low recovery capacity of the wells.

Results/Lessons Learned:

Due to the high electrical conductivity of the area, which reaches values of up to 50 mS/cm, the electrical current in the area averaged 5.6A. The results indicated a pumping influence radius of 8.0 m and electrokinetic technique influence at distances of up to 14.80 m. Regarding pH, it was observed that in the cathode well, there was an increase over the operation, reaching values above 3.5, while in the anode well, the pH showed a slight decrease, reaching a value of 1.5. Considering the flow during the test and the concentrations obtained in the effluent and precipitated material, it is estimated that 16 kg of metals were removed, consisting of 50% iron and 47% aluminum. The results allowed for the calculation of a mass removal rate for the two associated techniques of 4.11 kg per m³ pumped, and in relation to the material precipitated on the electrode, a rate of 0.11 g per day per electrode was observed. Thus, it was determined that the combination of these technologies has the potential for area remediation.

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Wagner Rodrigo