عنوان مقاله [English]
Abstract: It is proven that the financial benefits of using the proposed new tailings materials in terms of environmental sustainability are much higher when compared to normal materials. The research has been conducted to investigate the possible environmental problems of using iron ore mine tailings in civil engineering projects (road construction materials). Therefore, two main iron ore mine tailings of Gol-e-Gohar complex produced in magnetite and hematite plants were evaluated in terms of leaching heavy elements after application as road materials. To address the potential application of tailings as road materials, the main characteristics of tailings such as elemental analysis, pollution indicators, and engineering properties after stabilization by Portland cement were measured. The leaching of dangerous elements in a natural and stabilized state of compacted tailings at different times and pHs were assessed. The total amount of elements by ICP analysis showed that the Mn, Fe, Zn, Cd, Ni, and Cu are more abundant in the two tailings and their leaching must be tested. The general results showed that leaching with different leakage times and solutions at different pH have no effect on the release of elements through tailings, so their efficiency as road materials from an environmental point of view is acceptable providing meet the engineering standards as materials. In addition to leaching experiments, contamination, enrichment, and geo-accumulation indices also confirmed leaching results.
Methods and materials: Gol-e Gohar Mining Zone With its rich iron ore mines as one of the most prominent active mining poles in the Middle East. These mineral deposits are located in Kerman province, 50 km southwest of Sirjan city. Gol-e Gohar iron ore deposit is located in six separate anomalies with a reserve of about 1200 million tons in a range of approximately 10 km in length and approximately 4 km in width. Products extracted from this mine are: iron ore pellets, iron ore concentrate and granulated ore. ]. In this study, two iron ore tailings including magnetite and hematite tailings which has been collected from hematite and magnetite plants of Gol-e Gohar strict, where considered. Due to changes in feed conditions and operational problems, 75 tons per hour of hematite with dimensions less than 80 microns and 38% iron grade is transferred to the tailing dams.
Soil classification, Atterberg limits, specific gravity, compaction, unconfined compressive strength (UCS) and permeability tests were performed according to ASTM standard for raw and cement-stabilized tailings. Tailings were stabilized using 5% of Portland cement by weight of dry tailings and sample were compacted with standard energy cured for 28 days in plastic bags at room temperature. This percentage of Portland cement satisfied the minimum allowable unconfined compressive strength (2.1 MPa) for base materials. The total elements of tailings was measured by ICP Mass model ELAN 6100 DRC-e made by Perkin Elmer analysis. The composition of the elements as oxides was measured using an X-ray fluorescence spectroscope (XRF) model PW1410 made by PHILIPS Company, Netherlands.
The column was oriented vertically and slowly saturated from the top with deionized water. Then, the soil column was allowed to stabilize for 24 h. Experiments were conducted in triplicate at each pH (4.7, 7 and 9.5) and time (1 hour, 24 hours and one week) treatments. The water head was constant until the end of experiment. The leachate from the soil column was collected to determine the heavy metal concentrations by AAS apparatus model Analyst 800 made by Perkin Elmer. Enrichment factor, Contamination Factor, Pollution load index, Geo-accumulation Index were estimated.
Conclusion: The magnetite iron ore tailing was classified as SM and A-2-4 according to the USCS and AASHTO systems, respectively, while the hematite iron ore tailing was classified as ML and A-4 according to the USCS and ASSHTO systems, respectively.
Silicon, Mg, Al, Ca, Na, K are the most frequent elements in magnetite and hematite iron ore tailings, respectively. The most abundant rare elements in the magnetite iron ore tailing are Ce (40 ppm), La (28ppm), Nd (19.7 ppm) and in the hematite iron ore tailings are Ce (36 ppm), La (23 ppm) and Nd (17.2 ppm) which are in accordance with the earth’s crust levels.
Particle size of hematite iron ore tailing is finer of magnetite iron ore tailing. Therefore percentage of optimum moisture and the UCS value for hematite tailing is higher than that for magnetite tailing. Addition of Portland cement to iron ore tailings leads to an increase in the optimum moisture content and a decrease in the maximum dry density.
The amount of optimum moisture content (OMC) of magnetite iron ore tailing (11%) is lower than that for hematite iron ore tailing (13%) due to coarser particles. UCS of tailings followed the same trend, as well. The 5% of Portland cement (optimum amount) was added for stabilization of tailings and increasing the bearing capacity of these materials as road materials. After stabilization with Portland cement, the UCS of magnetite and hematite tailings increased from 0.349 MPa to 1.750 MPa and from 1.06 MPa to 3.160 MPa, respectively. The permeability coefficient of hematite tailings was 1.68 ×10-7 cm/s and magnetite tailings was 7.04 ×10 -7cm/s. The permeability coefficients of magnetite and hematite tailings after stabilization with Portland cement decreases to 2.64 ×10 -8 and 5.745 × 10 -7 cm /s, respectively. Therefore, it can be said that Portland cement results in reducing the permeability coefficient of tailings, because, coarse pores of tailings are filled with cement particles.
The rare earth elements (REE) form the largest chemically coherent group in the periodic table.. Though generally unfamiliar, the REE are essential for many hundreds of applications (occupy 41% of global consumption). The versatility and specificity of the REE has given them a level of technological, environmental, and economic importance considerably greater than might be expected from their relative obscurity. Values were obtained from solutions with concentrations in the range of ppm of 14 elements corresponding to REEs: La, Ce, Pr, Nd, Sm, Sc, Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu .
Leaching test showed that the release of elements was negligible, at different pH solutions and leaching times. In fact, the use of these tailings as materials in road construction may not cause environmental concern in regard with elemental leaching; therefore, they will be suggested as materials providing pass the technical and engineering standards.