ELECTROCHEMICAL TREATMENT OF THE ACID MINE DRAINAGE PRETREATED WITH CaO
VISNJA ORESCANIN1*, ROBERT KOLLAR1, KARLO NAD1, NENAD MIKULIC2, GORDANA MEDUNIC3
1 Advanced Energy Ltd., V. Prekrata 43, 10000 Zagreb, Croatia, Phone: +385-1-6535532; E-mail:
2EKO INVEST, Ltd., Draskoviceva 50, 10000 Zagreb, Croatia
3 Institute of Mineralogy and Petrography, Faculty of Science, Horvatovac 102a, 10000 Zagreb, Croatia
Acid Mine Drainage (AMD) originates in the reaction of sulfide minerals from an open pit or the mine tailings with water and oxygen creating sulfuric acid. This process is largely accelerated by the activity of Thiobacillus ferroxidans bacteria. Under the acidic conditions trace metals are liberated from the ore/tailings into solution causing acidification/heavy metals pollution of the surrounding soil, groundwater as well as rivers and streams that receiving such effluent. Consequently, this activity leads to the to the serious pollution of drinking water sources in the area of the influence as well as loss of the agricultural land which is not suitable for agricultural production due to the pollution with metals and high acidity.
The subject of this research was the characterization and the treatment of the acid mine drainage (AMD) originating from the sulfide ore mining and metallurgical activities in the Bor copper mining and smelting complex, Serbia. The AMD from the Bor mining complex (Bor-Krivelj-Cerovo) and smelting /refining of copper was characterized by low pH value (usually below 4) and high concentrations of heavy metals whose concentrations vary depending on the source. If entire complex was considered 7 different sources of the wastewaters could be defined. One of the sources is AMD from the “Robule” Lake which is the subject of presented study. The following values of the parameters in the AMD from the “Robule” Lake were determined: pH = 2.67, iron = 921.1 mg/L, copper = 91.7 mg/L, manganese = 107.3 mg/L, zinc = 58.6 mg/L, chromium = 12.3 mg/L and sulfates = 10830 mg/L.
The treatment of the AMD included pretreatment/pH adjustment with CaO until pH 8 followed by electrocoagulation using iron (I = 50 A; U = 10 V; t =5 min.)followed by aluminum electrode sets (I = 50 A; U = 10 V; t =10 min.). Each electrode set contained of ten quadratic, one millimeter thick plates (75 x 250 mm) in the parallel arrangement, separated by an electro insulator. The distance between plates was 10 mm in both electrode sets.In the end of electrochemical treatment the suspension was recirculated in strong electromagnetic field for 10 minutes and subjected to slow mixing for another 15 minutes while the settlement time was 30 minutes.
Following the combined treatment, the decrease in the initial concentration of heavy metals was up to 30557 times. The removal efficiencies for color, suspended solids (SS) and Cu was 100%, Cr, Mn, Fe, Co, Ni and Zn ranged from 99.91% to 99.99%, V, Pb, Hg and turbidity from 96.55% to 98.78% while the removal of sulfates and EC was 86.43% and 76.12%, respectively (Table 1). The removal efficiency of heavy metals increased with increasing initial concentration.
Table 1. Physical and chemical parameters determined in the acid mine drainage from the “Robule” Lake before and after the combined CaO /electrochemical treatment and removal efficiencies for each parameter.
Parameter / Initial effluent / Final effluent / Removal efficiency (%)Color (PtCo) / 743 / 0 / 100.00
Turbidity (NTU) / 30 / 1 / 96.67
SS (mg/L) / 10 / 0 / 100.00
EC (mS/cm) / 8.92 / 2.13 / 76.12
Sulfates (mg/L) / 10830 / 1470 / 86.43
Hg (mg/L) / 0.082 / 0.001 / 98.78
Pb (mg/L) / 0.043 / 0.001 / 97.67
V (mg/L) / 0.087 / 0.003 / 96.55
Cr (mg/L) / 12.341 / 0.004 / 99.97
Mn (mg/L) / 107.304 / 0.074 / 99.93
Fe (mg/L) / 921.130 / 0.047 / 99.99
Co (mg/L) / 0.119 / 0.001 / 99.16
Ni (mg/L) / 1.970 / 0.002 / 99.90
Cu (mg/L) / 91.671 / 0.003 / 100.00
Zn (mg/L) / 58.637 / 0.029 / 99.95
Waste sludge from the combined treatment process could be reused for another cycle of the pH adjustment/pretreatment of the acid mine drainage instead of CaO, and afterwards, due to its inertness, it could be used for overlaying layer of the flotation waste heap during its recovery work.