Because of the uniqueness of geological mineralization, tailings obtained from Chenchao Iron Mine have low SiO2 content of only 27.80%. Content of Al2O3 and MgO is 13.31% and CaSO4 is 22.09%. The fineness modulus of the ores is large enough for convenient mineral separation, thus resulting in 16.03% −5
Properties of tailings and agents in mineral processing flow sheet are often studied with respect to mine filling. For example, some mines have ultra-fine tailings that are easy to suspend and sediment slowly under natural conditions, thus making the feeding concentration and flow rate difficult to control. Under these circumstances, flocculants should be added to tailings to accelerate sedimentation and reach a high settling concentration in a short time, thus realizing high-concentration filling, which is easy to control [
Natural and flocculation settling experiments have been conducted for the sedimentation of ultra-fine tailings in numerous related studies. Through a contrast experiment of different flocculants and process control, the best flocculant and its application conditions have been determined [
For the concentration technology of extremely fine particle tailings which has been gradually developed in recent years, combined with the technical problems appearing in the field, new technologies, new equipment, and new materials have been applied to solve the difficult problems in the production. For example, in terms of the settlement and concentration of fine tailing, researchers calculated the size of the efficient thickener with the help of laboratory test results, and it played a good role in the concentration of copper tailing [
Considering the high gypsum content and slow sedimentation of ultra-fine tailings in Chenchao Iron Mine, natural and flocculant sedimentation experiments of tailings were conducted in this study to provide references for the future mass flow filling system of the mine. As the largest iron mine reserve in the mid-southern region of China, Chenchao Iron Mine is rich in high-quality iron ore reserves. Underground mining will be performed comprehensively after the open pit of the mine is closed to utilize local resources reasonably and sustainably.
Filling mining is essential for the future. Therefore, flocculation settling experiments of tailings should be conducted as they can offer technological parameters for the future introduction of deep-cone thickeners into filling systems. This study not only plays an important role in goaf management and reutilization of solid wastes in the Yangtze River basin but can also protect the local ecological environment and promote harmonious development between mine production and natural ecology.
The basic physical properties of the tailings are shown in Table
Physical properties of tailings.
Material | Special gravity | Bulk density (t/m3) | Dense porosity (%) | Angle of repose (°) |
Tailings | 2.77 | 1.590 | 42.60 | 33.73 |
The particle size distribution of tailings is shown in Figure
Particle size distribution curve of tailings.
The chemical composition of the tailings is shown in Figure
Chemical composition of tailings.
Special BASF flocculant (model no. Pheomax9010) for tailing settling, Germany BASF anionic flocculant with high molecular weight (model no. M342), Germany Anionic flocculant with 12,000,000 MW, Northern Chemistry Nonionic flocculant with 12,000,000 MW, Northern Chemistry
In the experiments, common tap water at room temperature and pH = 7 was used to prepare the tailing slurry and flocculant solution.
The initial concentration of the tailing slurry was 40%, and the concentration of the flocculant solution was 3‰. The flocculant dosage per ton of the dry tailings was 20 g/t of the flocculants Pheomax9010 BASF and M³42 BASF and 40 g/t of the anionic flocculant with 12,000,000 MW (Northern Chemistry) and the nonionic flocculant with 12,000,000 MW (Northern Chemistry).
The particle size, shape, and chemical composition of tailings can influence the settling characteristics of tailing slurry considerably. These parameters determine the stacking state and settling concentration and bulk density of tailings. The tailings in Chenchao Iron Mine are difficult to sediment, except in natural sedimentation experiments. Thus, flocculating sedimentation experiments using four different flocculants were conducted in this study with the aim of recognizing the best flocculant for tailing settling. Changes in supernate volume in a 1000 ml cylinder were recorded; according to the recorded data, the net water growth and variations in settling concentration and bulk density were calculated. The details of the experimental programs are listed in Table
Natural and flocculating sedimentation experiments of tailings.
Experiment no. | Test type | Name of flocculants | Concentration of flocculant solution (‰) | Flocculant dosage per ton of dry tailing (g/t) | Initial concentration of tailing slurry (%) |
---|---|---|---|---|---|
#1 | Natural sedimentation | No flocculant | — | — | 40 |
#2 | Flocculating sedimentation | Pheomax9010 BASF | 3 | 20 | 40 |
#3 | Flocculating sedimentation | M³42 BASF | 3 | 20 | 40 |
#4 | Flocculating sedimentation | Anionic flocculant with 12,000,000 MW (Northern Chemistry) | 3 | 40 | 40 |
#5 | Flocculating sedimentation | Nonionic flocculant with 12,000,000 MW (Northern Chemistry) | 3 | 40 | 40 |
The natural sedimentation experiment, which used no flocculants and tested the sedimentation process of tailings under natural conditions, was compared with flocculating sedimentation. The initial concentration of the tailing slurry was 40%. Combined with the technological parameters in the future daily filling production process, the concentration of tailing mortar transported from the dressing plant to the filling slurry preparation station is about 40%, so the preparation concentration of the tailing mortar of this group is 40%.
The variations in the natural sedimentation test parameters of the tailings are shown in Figure
Natural sedimentation test parameters of tailings (#1).
The variation curves of the settling concentration and bulk density of the tailings under natural conditions are shown in Figure
Variation curves of natural settling concentration and bulk density (#1).
In this experiment, Pheomax9010 BASF at a dosage of 20 g/t was used as the flocculant. The concentration of the flocculant solution was 3‰, and the initial concentration of the tailing slurry was 40%. Combined with the technological parameters in the future daily filling production process, the concentration of tailing mortar transported from the dressing plant to the filling slurry preparation station is about 40%, so the preparation concentration of the tailing mortar of this group is 40%.
The variations in the flocculating sedimentation test parameters of the tailings with Pheomax9010 BASF are shown in Figure
Flocculating sedimentation test parameters of tailings (#2).
The variation curves of the settling concentration and bulk density of the tailings with Pheomax9010 BASF are shown in Figure
Variation curves of flocculation settling concentration and bulk density (#2).
In this experiment, M342 BASF at a dosage of 20 g/t was used as the flocculant. The concentration of the flocculant solution was 3‰, and the initial concentration of the tailing slurry was 40%.
The variations in the flocculating sedimentation test parameters of the tailings with M³42 BASF are shown in Figure
Flocculating sedimentation test parameters of tailings (#3).
The variation curves of the settling concentration and bulk density of the tailings with M³42 BASF are shown in Figure
Variation curves of flocculation settling concentration and bulk density (#3).
In this experiment, the anionic flocculant with 12,000,000 MW (Northern Chemistry) at a dosage of 40 g/t was used. The concentration of the flocculant solution was 3‰, and the initial concentration of the tailing slurry was 40%.
Figure
Flocculating sedimentation test parameters of tailings (#4).
Figure
Variation curves of flocculation settling concentration and bulk density (#4).
In this experiment, the nonionic flocculant with 12,000,000 MW (Northern Chemistry) at a dosage of 40 g/t was used. The concentration of the flocculant solution was 3‰, and the initial concentration of the tailing slurry was 40%.
The variations in the flocculating sedimentation test parameters of the tailings with the nonionic flocculant with 12,000,000 MW (Northern Chemistry) are shown in Figure
Flocculating sedimentation test parameters of tailings (#5).
The variation curves of the settling concentration and bulk density of the tailings with the nonionic flocculant with 12,000,000 MW (Northern Chemistry) are shown in Figure
Variation curves of flocculation settling concentration and bulk density (#5).
The times for reaching the final settling, maximum settling concentration, and maximum settling bulk density of the five experiments were analyzed. The flocculants were ranked on the basis of the required final settling concentration of 55% (Table
Statistics on parameters at final settling.
Test no. | Time for reaching the final settling (min) | Maximum settling concentration (%) | Maximum settling bulk density (t/m3) | Order of flocculants |
---|---|---|---|---|
#1 | 120 | 66.67 | 1.667 | Standard |
#2 | 40 | 60.98 | 1.577 | 1 |
#3 | 180 | 62.50 | 1.600 | 3 |
#4 | 60 | 62.50 | 1.600 | 2 |
#5 | 120 | 64.10 | 1.625 | 4 |
Curves of settling concentration and bulk density (30 min).
Curves of settling concentration and bulk density (60 min).
Curves of settling concentration and bulk density (90 min).
Curves of settling concentration and bulk density (120 min).
As shown in Table
The comparison of the four flocculating sedimentation experimental results shows that different flocculants cause tailings to show different settling characteristics. Pheomax9010 BASF (20 g/t) achieved the highest settling speed, followed by the anionic flocculant with 12,000,000 MW (Northern Chemistry) (40 g/t), nonionic flocculant with 12,000,000 MW (Northern Chemistry) (40 g/t), and M³42 BASF (20 g/t). The sequence of final settling concentration from large to small is natural sedimentation (66.67%), nonionic flocculant with 12,000,000 MW (Northern Chemistry) (64.18%), anionic flocculant with 12,000,000 MW (Northern Chemistry) (62.5%), M342 BASF (62.53%), and Pheomax9010 BASF (61.12%). The future filling technique only requires a settling concentration of tailings of at least 55% hence, the flocculant that can reach 55% settling concentration in the shortest time is the best. The experimental results show that using Pheomax9010 BASF, the settling concentration of the tailing slurry could reach 55% in 40 min, thus indicating that Pheomax9010 BASF is the optimal flocculant material for tailing settling in Chenchao Iron Mine. The anionic flocculant with 12,000,000 MW (Northern Chemistry), could lead to a 55% settling concentration in 60 min, is the second best.
In summary, although natural sedimentation took a long time to reach the final settling state, the settling concentration and bulk density in this setting were relatively high and accompanied with tight tailing stacking structures. The supernate was light grey during the settling process, was not clear in the beginning, and became transparent in the final settling state. The natural sedimentation images show that the slurry volume under natural sedimentation was the highest in the beginning but became the lowest in the end, thus resulting in high settling concentration and bulk density. Under natural conditions, 120 min was needed to reach the final settling state. The final settling concentration was 66.67%, and the final settling bulk density was 1.667 t/m3.
The comparison of the flocculating experiments shows that the tailing slurry has high sedimentation speed. The supernate can become transparent in a short time and was most transparent when Pheomax9010 BASF was used. Furthermore, the final settling state and the best settling performance were achieved in the shortest time when this flocculant was used. The images show that the tailings became relatively fluffy at their final settling. The slurry volumes in all flocculating experiments were higher than that under natural sedimentation, thus resulting in relatively smaller settling concentration and bulk density. Pheomax9010 BASF achieved the smallest settling concentration and bulk density, reaching the final settling state in only 40 min. The final settling concentration was 60.98%, and the final settling bulk density was 1.577 t/m3. These parameters can meet settling requirements. The required ≥55% settling concentration meant that the key to evaluating the performances of the flocculating materials was the time. Therefore, Pheomax9010 BASF is the best flocculant for Chenchao Iron Mine.
The settling performance of tailings often influences the tailing filling system considerably. With slow sedimentation of tailings, preparing high-concentration filling slurry and meeting the required physical properties, such as strength of fill, are difficult. The sedimentation of tailings is often influenced by their properties. An appropriate amount of flocculant is often needed for tailings with special properties and slow settling. Jiao et al. determined the best flocculant through flocculating sedimentation experiment of tailings. Consequently, the tailing slurry reached the desired concentration and the prepared strength of fill could meet mining requirements [
To provide references for future filling system design and environment-friendly treatment of abundant solid waste, the optimal flocculant was chosen by the current study considering the difficult settling of ultra-fine iron tailings with rich gypsum. Tailing slurry in the future filling system for Chenchao Iron Mine will be prepared with a deep-cone thickener. Hence, related studies that combine properties of tailings shall be conducted. In mines with tailing filling, sedimentation properties of tailings are important in technique connection, working efficiency, and comprehensive effect of enterprises. Filling techniques with tight technique connection, few errors, and high efficiency are important in enterprise development and competition. Therefore, a method that allows for the quickest settling of tailings should be developed to provide technological references for increasing the preparation efficiency of filling slurry.
A large area in the Yangtze River basin in China has ore mines. Solid wastes from mining production are stacked in the surface tailing pond and migrate outside through natural factors, such as wind and rain, thus causing potential risks to surrounding land, rivers, and underground water. Hence, effective measures should be adopted to avoid surrounding environmental pollution by heavy metals and other harmful elements in solid waste. As an ultra-large mine in the Wuhan economic circle and along the Yangtze River basin, Chenchao Iron Mine has a long exploitation history. The water and land resources in the Yangtze River basin should thus be protected through the proper disposal of solid waste. Meanwhile, goaf filling engineering is used for the reutilization of solid wastes; hence, studying the sedimentation properties of tailings can provide early technological parameters for filling engineering. Consequently, discussing the flocculating sedimentation performances of ultra-fine iron tailings with rich gypsum is important as it aims to protect the ecological environment in the Yangtze River basin.
In Chenchao Iron Mine, about 2711 m3 goaf volume arises every day. However, the existing conventional flow filling system can only fill 750 m3 and make selective filling to goaf. The tailing dosage is 745 t/d. The dosage of tailings for comprehensive filling exploitation in the future will increase dramatically to 2692 t/d; thereby, it considerably reduces the stacking amount of tailings in the surface tailing pond. The service life of the tailing pond will thus be prolonged, and tailing emission and disposal cost will be reduced dramatically.
Tailings of Chenchao Iron Mine contain some gypsum and a small number of quartz, which have strong sandiness and easily sink. Moreover, the tailings have a low natural settling rate due to the ultra-fine size of particles, which make the final dense settling state difficult to reach in a short time without a flocculant. A contrast analysis between the natural and flocculating sedimentation of tailings was conducted on the basis of the properties of the tailings in Chenchao Iron Mine. The Pheomax9010 BASF was the most effective. Compared to other flocculants, it can decrease 80 mins to achieve the same settling concentration and settling bulk density.
As shown in the flocculating sedimentation images, the supernate of experiment was the clearest at 30 min and the sedimentation of tailings was the quickest without the suspending particles. Even the ultra-fine particles sedimented with large ones. The settling concentration of the tailings in experiment was not the highest at 40 min but still meets the concentration limit of 55%. Therefore, Pheomax9010 BASF is recommended as the flocculating sedimentation of tailings in the future.
In the future study of tailings materials, they can be classified according to the detailed grading of granular material; the tailings with special particle size distribution are divided to the size of the corresponding category. Combined with the specific use of tailings materials, mesoscopic and microscopic analysis is conducted to investigate the relationship of particle shape and the settling velocity and to obtain the analytical expression of the granular material sedimentation process to the analysis of the related laws and prediction.
As the largest iron mine reserve in the mid-southern region of China, it has a long history of exploitation. The long-term caving exploitation has accumulated great goaf space, and surfaces in some regions have collapsed, thus serious risks exist. Chenchao Iron Mine is the main mine for Wuhan Steel Inc. For goaf management and environment-friendly treatment of solid wastes, Chenchao Iron Mine will gradually use filling mining pattern. This study is a preliminary exploration that provides basic parameters for its future filling system design. The results of this study will be used to guide the goaf management and environment-friendly treatment of solid wastes in the Yangtze River basin.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare no conflicts of interest concerning the publication of this paper.
Daiqiang Deng wrote the main text of the manuscript. Guodong Cao collected and analyzed the data. All authors reviewed and commented on the manuscript.
This work was supported by the NSFC projects of China (51764009), the Guizhou Province Science and Technology Support Plan Project (Grant no. [2018]2836), the Provincial Natural Science Foundation of Hunan (2020JJ5538), the Scientific Research Fund of Hunan Province Education Department (20A475 and 19C1736), and the High-Level Talent Gathering Project in Hunan Province (2019RS1059). The authors are grateful for the financial support for this research.