Mehdi Zare, Ali Moradzadeh, Abolghasem Kamkar-Rouhani, Faramarz Doulati-Ardejani,
Volume 14, Issue 3 (11-2020)
Introduction
"Sulfide-carbonate" deposit is a term, which comprises a series of sulfide minerals such as Zn-Pb ore minerals, mainly considered as related to weathering of Zn-Pb sulfide concentrations and influence in sedimentary hosts (carbonate). There are more than 350 Zn-Pb deposits located in Iran, including world-class deposits such as Angouran, Mehdiabad and Irankouh. Due to the mining activity of these deposits, it creates a significant amount of mine waste that releases
of these wastes in the environment causing severe problems. One of the main problems is the formation of Acid Mine Drainage (AMD). AMD is produced by oxidation of sulphide minerals, particularly pyrite (FeS2) in waste dump. Due to low pH and the ability to dissolve metals and other compounds, it can host a number of environmental problems. A phenomenon known as natural or alkaline mine drainage (NAMD) occurs at high pH values when the neutralizing minerals are significantly present in the mine waste or when the oxidation of the sulfide minerals is poor. However, the metals and cationic species, such as Cu, Pb and Cd, are more soluble at low pH. In contrast, elements that form anionic species, such as Se, Cr, V, and Mo, tend to be more soluble at high pH and Ni, Zn, Co, As, and Sb, are soluble at near-neutral pH, and can potentially contaminate mine effluents, even without acidic conditions. Therefore Acid or Neutralization potential
(AP&NP) of waste dump
is significantly affects on the composition, transfers and fates of contaminati
ons transmitted from waste dump. The aim of this study was to monitoring heavy metals concentrations and assessments of pollution potential of waste dumps in Anguran mine by static method and has been compared by mineralogical approach.
Material and methods
The Angouran Zn-Pb deposit is located in the 135 kilometers southwest part of Zanjan Province, NW Iran. This area belongs to the northwestern part of the Sanandaj-Sirjan Zone, a metamorphic belt related to the Zagros orogeny. Angouran mine is one of the most important carbonate hosted Zn-Pb deposits in Iran that mining activity has been created a significant amount of waste dump in around pit. To achieve the goals, the 47 samples taken from different surficial parts of the waste dump were analyzed by using the ICP-MS method to determine the concentration of elements and heavy metals. These elements and metals includes: Ca, Mg, S and As, Cd, Cr, Cu, Ni, Pb, Zn. The pollution index (PI) were modeled for heavy metal contamination risk zoning then modified Acid Base Accounting (ABA) static method was used to evaluate of acid and neutralization potential (AP&NP) of the waste dump samples and the results were modeled by Kriging method. At the end, mineralogical approach (Mg + Ca concentration) was used to determine the source of neutralization and to better interpret the static results.
Results and discussion
The results of contamination index showed that zinc, arsenic and cadmium had the highest average contamination index (18.89, 12.13 and 5.8, respectively) and the trend of total metal changes in the region as Zn> As> Cd> Pb > Ni> Cr> Cu was rated.
Datas measured in modified ABA method were modeled in 2D maps using the Kiriging method. Due to the low total sulfur content (less than 1%), all of the samples were Net Neutralization Potential (NNP) with a range of 49- 990 kg calcium carbonate per ton, and the study area was classified into three neutralization potential (NP), High (NP) and Very High (NP) levels. The mineralogical approach (Mg + Ca concentration) was used as a useful tool for better interpretation of modified ABA results and determines the neutralizing source. Mineralogical approach results indicate that calcite species are the main source of neutralization and have high correlation coefficient (R = 0.99) with the modified ABA method. In order to validate the results, the presence of mineral calcite was confirmed by XRD analysis on 4 samples.
Assessment of AP and NP of sulfide – carbonate waste dump in this research can be used as a basis model for other similar mines to control environmental problems and to identify the behavior and to transfer heavy metals in mine drainage in the future. Mineralogical approach results show that neutralizing potential and neutralizing source can be obtained without using expensive mineralogy analyses in this type of carbonate-sulfide deposit
