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Vol. 7. Num. 1.January - March 2018
Pages 1-102
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Vol. 7. Num. 1.January - March 2018
Pages 1-102
Review Article
DOI: 10.1016/j.jmrt.2017.04.007
Effect of calcium ion on the separation of rhodochrosite and calcite
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Na Luo
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luona1986210@163.com

Corresponding author.
, De-zhou Wei, Yan-bai Shen, Wen-gang Liu, Shu-ling Gao
College of Resources and Civil Engineering, Northeastern University, Shenyang, China
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Table 1. Results of separation of rhodochrosite and calcite.
Table 2. Reaction of Ca2+ and equilibrium constant in the system of CaCO3.
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Abstract

The effect of calcium ion on the separation of rhodochrosite and calcite was systematically investigated based on flotation tests, zeta potential measurements, and scanning electron microscopy analysis. The flotation results showed that the separation of rhodochrosite and calcite was inefficient due to rhodochrosite and calcite being similar in many physical and chemical properties, which could make the separation of rhodochrosite from calcite inefficient. The separation of rhodochrosite and calcite can be significantly improved by adding sodium hexa metaphosphate (SH) because SH could depress calcite flotation while it did not bring an impact on rhodochrosite flotation. However, when calcium ion was added into this flotation system, the separation of rhodochrosite and calcite deteriorated as SH also depressed rhodochrosite flotation under this condition. The solution chemical calculation and scanning electron microscopy analysis illustrated that the formation of calcite precipitation coated on the rhodochrosite surface was the main reason because calcium ion increased the depression effect of SH on rhodochrosite.

Keywords:
Rhodochrosite
Calcite
Calcium ion
Flotation
Separation
Full Text
1Introduction

As the primary source of manganese, pyrolusite is steadily getting depleted and rhodochrosite (MnCO3) becomes one of the major sources of manganese oxide. Although manganese carbonate resources are very rich in China, there are fewer and fewer high-quality resources due to the over-exploitation of manganese ore. To meet manganese market demand in the future, it is significant to develop low-grade rhodochrosite for a marketable product. Especially, the flotation is one of the most effective methods to increase the recovery of fine grained and low-grade rhodochrosite.

Calcite is one of the most common and important components in sedimentary rocks. And calcite is an extensive carbonate gangue in the flotation of rhodochrosite, smithsonite, celestite and apatite [1–3]. It is easy to enter the rhodochrosite flotation concentrate because of naturally hydrophobic, thus reducing concentrate grade [4]. Being a calcium type gangue mineral, large quantities of calcite in flotation concentrates can cause problems during smelting. Rhodochrosite and calcite are calcite-group minerals that show similar flotation behavior due to the same crystal structure and similar chemical composition. Therefore, it is difficult to achieve effective separation of rhodochrosite from calcite in conventional flotation. Flotation separation of valuable carbonate minerals and calcite is extremely complex because of the interaction between minerals and dissolved metal ions.

The dissolution characteristics of rhodochrosite and calcite play an important role in determining the interactions occurred in the bulk solution or on the mineral surfaces [2,5]. The dissolved species of minerals could participate in some reactions such as hydrolysis, complexation, adsorption, and bulk precipitations, which could affect the selective interaction between reagent and mineral [6–8]. In addition, some agents such as CaO, which is used as pH regulator and the water used in actual production also increase the content of the cations, which also effect rhodochrosite flotation in the pulp. Although some reagents such as starch, sodium hexa methaphosphate (SH), and sodium silicate are usually used as calcite depressants in rhodochrosite flotation, the separation process shows relatively low selectivity in practice due to their similar surface properties and dissolved species [9–11]. Moreover, few literatures are focused on the effect of metal ions on flotation separation of rhodochrosite and calcite.

In this study, the effect of calcium ion (Ca2+) on the separation of rhodochrosite and calcite was investigated. The flotation tests were used to examine the flotation regularity of rhodochrosite and calcite in the absence and presence of Ca2+. To clarify the reasons on the difficulty in flotation separation of rhodochrosite and calcite, the electro-kinetic zeta potential measurements, solution chemistry calculations, scanning electron microscopy, accompanying with the flotation results, were systematically carried out.

2Experimental2.1Samples and reagents

Both calcite and rhodochrosite used in this study were obtained from Changsha, Hunan Province, China. The results of mineralogy and X-ray powder diffraction confirmed that the purity of both samples was higher than 95%. The obtained samples were ground and then sieved to collect the −100μm fraction for the microflotation and scanning electron microscopy tests. Hydrochloric acid (HCl) and sodium carbonate (Na2CO3) were used as pH regulators. Sodium oleate (NaOL) and sodium hexametaphosphate (SH) were used as collector and depressant, respectively. Calcium chloride (CaCl2) was dissolved to prepare a predefined concentration of Ca2+ solution. All the reagents used in this study were of analytical grade. The water used in actual production has a certain degree of hardness. A certain amount of calcium and magnesium ions in water, which also affect the flotation separation of rhodochrosite and calcite. In order to eliminate the effect of ions in water on rhodochrosite flotation, for researching convenience, deionized double distilled water was used for all tests.

2.2Flotation tests

Single mineral flotation tests were carried out in a mechanical agitation flotation machine. The impeller speed was fixed at 1800r/min. The mineral suspension was prepared by adding 2.0g of minerals to 40mL of solutions. The pH of the mineral suspension was adjusted to a desired value using Na2CO3 or HCl. The slurry was conditioned for 3min after adding the depressant of SH. Subsequently, the collector of NaOL was introduced into the slurry for 3min and then flotation was carried out for a total of 3min. The floated and tailing fractions were collected separately and dried and weighed for calculations.

2.3Zeta potential measurements

The samples used for zeta potential measurements were prepared as follows. The samples of 20mg in the size −5μm were added to desired amounts of solution and then magnetically stirred for 10min, and adjusted pH using HCl or Na2CO3. Zeta potential measurements of rhodochrosite were carried out using a zeta plus potential meter. At each condition, the zeta potentials of minerals were measured and an average value of three individually measurements was accredited. Potassium nitrate was used to maintain the ionic strength at 10−3mol/L.

2.4Scanning electron microscopy

A scanning electron microscope (SEM, CAMSCAN CS44FE) equipped with an energy dispersive X-ray spectrometer (EDS) was used to observe the morphology and characterize the elemental composition of the rhodochrosite samples. The samples used for SEM observation were prepared with the same conditioning regime as the flotation tests, and then filtrated and washed thoroughly with deionized double distilled water. The prepared samples were dried in a vacuum oven at 25°C for 24h.

3Results and discussion3.1Effect of Ca2+ on the separation of rhodochrosite and calcite

The effect of pH on the flotation recovery of rhodochrosite and calcite is shown in Fig. 1. As shown in this figure, the flotation recoveries of rhodochrosite and calcite were very high over the entire pH range tested. Such high recovery could be attributed to the chemisorptions of oleate on rhodochrosite and calcite at alkaline conditions [12,13]. The flotation recoveries of rhodochrosite and calcite increased slightly as the pH increased. According to the results shown in Fig. 1, it can be concluded that it is difficult to separate rhodochrosite and calcite without the addition of depressant.

Fig. 1.
(0.06MB).

Effect of pH on the flotation recovery of rhodochrosite and calcite (c(NaOL)=1×10−4mol/L).

The effect of pH on the floatability of rhodochrosite and calcite in the presence of SH is shown in Fig. 2. The results illustrated that SH had a significant depression effect on calcite in the pH range of 7–12. The recovery of calcite decreased from 90% to 20% in the absence and presence of SH at pH 11. Different from calcite, the rhodochrosite flotation was not obviously influenced by SH addition at alkaline conditions. The rhodochrosite was depressed by SH addition when pH further decreased. Therefore, it is possible to separate rhodochrosite and calcite at alkaline conditions by using SH as depressant.

Fig. 2.
(0.07MB).

Effect of pH on the flotation of rhodochrosite and calcite in the presence of SH (c(NaOL)=1×10−4mol/L and c(SH)=20mg/L).

In order to investigate whether SH is suitable for separating calcite from rhodochrosite, the samples of rhodochrosite and calcite were mixed by mass ratio of 1:1 and floated at pH 11 using NaOL and SH as collector and depressant, respectively, and the result is presented in Table 1. In the mixed sample, the theory grades of Mn and Ca are 23.91% and 20.00%, respectively. The results showed that the grades of Mn and Ca in the concentrate were only slightly different from those in raw ore, illustrating that it is unfavorable to separate rhodochrosite and calcite by using SH as depressant. Therefore, it demonstrates that there are some other factors to affect the flotation separation of rhodochrosite and calcite in the mixed minerals slurry.

Table 1.

Results of separation of rhodochrosite and calcite.

SH concentration (mg/L)  Product  Productivity (%)  Mn grade (%)  Ca grade (%)  Mn recovery (%)  Ca recovery (%) 
Concentrate  98.66  24.03  20.06  98.68  98.71 
  Tailing  1.34  23.71  19.83  1.32  1.29 
  Raw ore  100  24.02  20.05  100  100 
20  Concentrate  80.33  25.78  19.46  87.53  75.52 
  Tailing  19.67  14.98  25.76  12.47  24.48 
  Raw ore  100  23.66  20.70  100  100 
40  Concentrate  75.33  26.17  18.11  80.56  69.85 
  Tailing  24.67  19.28  23.88  19.44  30.15 
  Raw ore  100  23.90  19.53  100  100 

Salt-type minerals are commonly characterized by their higher solubility in water, where the extent of dissolution is remarkably higher than in most oxide/silicate systems. The dissolved species from one mineral frequently undergo hydrolysis or chemical reaction with other mineral surface in pulp, resulting in surface conversion of mineral and subsequently surface properties and flotation performance, making it difficult to separate such minerals without additional treatment [14].

The effect of Ca2+ on the depression of rhodochrosite (Fig. 3(a)) and calcite (Fig. 3(b)) using SH as depressant is shown in Fig. 3. As shown in Fig. 3(a), it can be seen that the addition of Ca2+ significantly affected rhodochrosite flotation in the pH range of 7–11.5, especially at pH 10, of which the rhodochrosite recovery decreased from 92% to 60%. It should be noted that a strange phenomenon in Fig. 3(a) is that the addition of Ca2+ increased the depress effect of SH on rhodochrosite flotation. The higher the pH, the stronger the depression effect. Different from the rhodochrosite, the result in Fig. 3(b) showed that the depression effect of SH on calcite was not influenced by Ca2+. These results illustrate that the presence of Ca2+ interferences with the separation of rhodochrosite and calcite.

Fig. 3.
(0.17MB).

Effect of Ca2+ on the depression of rhodochrosite and calcite in the presence of SH (c(NaOL)=1×10−4mol/L, c(Ca2+)=5×10−4mol/L and c(SH)=20mg/L).

Fig. 4 shows the effect of SH concentration on the flotation performance of rhodochrosite and calcite in the absence and presence of Ca2+. It showed that the separation of rhodochrosite and calcite could be realized at a concentration of 120mg/L in the absence of Ca2+. However, both rhodochrosite and calcite are depressed by SH in the presence of Ca2+.

Fig. 4.
(0.1MB).

Effect of SH concentration on the depression of rhodochrosite and calcite in the absence and presence of Ca2+ (c(NaOL)=1×10−4mol/L and c(Ca2+)=5×10−4mol/L).

3.2The depression mechanism of Ca2+ to rhodochrosite flotation

The Ca2+ could participate in some reactions such as hydrolysis, complexation, adsorption, and even surface or bulk precipitation [15,16]. The complex equilibria involving all such reactions can be expected to determine the interfacial properties of the particles and their flotation behaviors. The concentrations of each species were calculated based on various solution equilibria of the ions. The corresponding results are plotted as logC–pH diagram as shown in Fig. 5. The reactions for controlling the system of CaCO3 are listed in Table 2.

Fig. 5.
(0.07MB).

Effect of pH on hydrolysis species distribution of Ca2+ in the system of CaCO3 (CCa=2.0×10−4mol/L).

Table 2.

Reaction of Ca2+ and equilibrium constant in the system of CaCO3.

Equilibria equation  Equilibria constant 
CaCO3(s)=Ca2++CO32−  −8.35 
Ca2++CO32−=CaCO3(aq)  3.06 
Ca2++OH=Ca(OH)+  1.4 
Ca2++2OH=Ca(OH)2(aq)  2.77 
Ca(OH)2(s)=Ca2++2OH  −5.22 
H++CO32−=HCO3−  10.33 
H++HCO3−=H2CO3  6.35 

The species distribution diagrams can be calculated according to the equilibria equation and the results are shown in Fig. 5. The results illustrated that the CaCO3 precipitation began to form when pH was above 9.8, while Ca(OH)2 precipitation was not generate.

In order to further confirm whether Ca2+ formed precipitation and adsorbed on the surface of rhodochrosite or not, SEM-EDS analysis of rhodochrosite samples treated by Ca2+ and Na2CO3 were measured and the results are shown in Fig. 6. It was found that CaCO3 precipitations were coated on the surface of rhodochrosite in SEM image. Particularly, the spectrum showed that the peaks Ca and Mn were surely existed, confirming that CaCO3 precipitations were formed on the surface of rhodochrosite.

Fig. 6.
(0.28MB).

SEM image and EDS spectrum of rhodochrosite (rhodochrosite+Ca2++Na2CO3).

As a direct surface chemistry investigation of the mineral, electro-kinetic studies were undertaken to rhodochrosite at different conditions as a function of pH in 10−3M KNO3. Fig. 7 shows the effect of NaOL on the zeta potential of rhodochrosite in the absence and presence of Ca2+. The zeta potential of rhodochrosite negatively increased as the pH increased from 7.5 to 11.30 without Ca2+ addition for Line 1, indicating that collector ion of NaOL adsorbed on the surface of rhodochrosite. Such result is consistent with the flotation results shown in Fig. 1. Lines 2 and 3 are the zeta potential curves in the presence of Ca2+ without and with NaOL, respectively. It was found that the addition of NaOL had a negligible effect on zeta potential of rhodochrosite, indicating that the adsorption of collector ion on the surface of rhodochrosite did not occur at this condition.

Fig. 7.
(0.05MB).

Zeta potentials of rhodochrosite at different conditions. 1 – rhodochrosite+SH+NaOL; 2 – rhodochrosite+Ca2++SH; 3 – rhodochrosite+Ca2++SH+NaOL.

Based on the results of floatation tests and surface analysis, it can be concluded that Ca2+ is formed to CaCO3 precipitation and subsequently adsorbs on the surface of rhodochrosite. Although SH addition has little effect on rhodochrosite, the results indicate that CaCO3 precipitation coated on the surface of rhodochrosite makes rhodochrosite surface property similar to calcite in response to SH addition. And there is not only Ca2+ dissolved from calcite, some reagents and water used in flotation process may also increase the content of Ca2+ in pulp. The influence of these calcium ions on the flotation separation of rhodochrosite and calcite cannot be ignored. Therefore, a novel way is expected to be proposed by preventing Ca2+ from forming precipitation and coating on the surface of rhodochrosite in order to achieve effective flotation separation of rhodochrosite and calcite. The flotation methods and corresponding mechanisms are still unknown now, which will be further investigated in the near future.

4Conclusions

  • (1)

    The rhodochrosite and calcite are difficult to be separated without the addition of depressant as they are similar in many physical and chemical properties.

  • (2)

    SH is an effective reagent for the separation of rhodochrosite and calcite as SH depressed calcite floatation, while it did not affect the rhodochrosite flotation.

  • (3)

    The presence of Ca2+ increased the depression effect of SH on rhodochrosite, which was unfavorable for the separation of rhodochrosite and calcite.

  • (4)

    The formation of CaCO3 precipitation coated on the surface of rhodochrosite made the separation performance deteriorated because Ca2+ increased the depress effect of SH on rhodochrosite.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

The authors acknowledge the support of Fundamental Research Funds for the Central Universities (N130301003) and National Natural Science Foundation of China (51474054).

References
[[1]]
S.H. Hosseini,E. Forssberg
Smithsonite flotation using mixed anionic/cationic collector
Miner Process Extr Metall, 118 (2009), pp. 186-190
[[2]]
Q. Shi,Q.M. Feng,G.F. Zhang,H. Deng
Electrokinetic properties of smithsonite and its floatability with anionic collector
Colloids Surf A: Physicochem Eng Asp, 410 (2012), pp. 178-183
[[3]]
T. Takamori,M. Tsunekawa
Separation of calcite from fluorite ore by the adsorption washing flotation method
CIM Bull, 75 (1982), pp. 80
[[4]]
S.X. Song,S.C. Lu
A study on interflocculation and chemical dispersibility of extremely fine rhodochrosite with quartz and calcite
Min Metall Eng, 8 (1988), pp. 16-20
[[5]]
P. Van Cappellen,L. Charlet,W. Stumm,P. Wersin
A surface complexation model of the carbonate mineral–aqueous solution interface
Geochim Cosmochim Acta, 57 (1993), pp. 3505-3518
[[6]]
A.P.L. Nunes,A.E.C. Peres,A.C. De Araujo,G.E.S. Valadão
Electrokinetic properties of wavellite and its floatability with cationic and anionic collectors
J Colloid Interface Sci, 361 (2011), pp. 632-638 http://dx.doi.org/10.1016/j.jcis.2011.06.014
[[7]]
H.U. Sø,D. Postma,R. Jakobsen,F. Larsen
Sorption of phosphate onto calcite; results from batch experiments and surface complexation modeling
Geochim Cosmochim Acta, 75 (2011), pp. 2911-2923
[[8]]
D.R. Vučinić,D.S. Radulović,S.Đ. Deušić
Electrokinetic properties of hydroxyapatite under flotation conditions
J Colloid Interface Sci, 343 (2010), pp. 239-245 http://dx.doi.org/10.1016/j.jcis.2009.11.024
[[9]]
M. Ejtemaei,M. Irannajad,M. Gharabaghi
Influence of important factors on flotation of zinc oxide mineral using cationic, anionic and mixed (cationic/anionic) collectors
Miner Eng, 24 (2011), pp. 1402-1408
[[10]]
M. Irannajad,M. Ejtemaei,M. Gharabaghi
The effect of reagents on selective flotation of smithsonite-calcite-quartz
Miner Eng, 22 (2009), pp. 766-771
[[11]]
A.H.N. Kashani,F. Rashchi
Separation of oxidized zinc minerals from tailings: influence of flotation reagents
Miner Eng, 21 (2008), pp. 967-972
[[12]]
W.Q. Qin,S. Zou,S.J. Liu,H.L. Luo,R.Z. Liu,X.J. Wang
Solution chemistry mechanism of flotation of sodium oleate on rhodochrosite
J Wu Han Univ Technol, 36 (2014), pp. 124-129
[[13]]
Y.H. Hu,D.Z. Wang
Mechanism of fatty acid sodium flotation of salt-type minerals – a study
Min Metall Eng, 10 (1990), pp. 20-23
[[14]]
Y.H. Hu,J. Xu,C.Q. Luo,C. Yuan
Solution chemistry studies on dodecylamine flotation of smithsonite/calcite
J Central South Univ Technol, 26 (1995), pp. 589-594
[[15]]
F. Ikumapayi,M. Makitalo,B. Johansson,H.K. Rao
Recycling of process water in sulphide flotation: effect of calcium and sulphate ions on flotation of galena
Miner Eng, 39 (2012), pp. 77-88
[[16]]
Q. Shi,Q.M. Feng,G.F. Zhang,H. Deng
A novel method to improve depressants actions on calcite flotation
Miner Eng, 55 (2014), pp. 186-189

Na Luo is studying for a doctorate of mineral processing engineering at Northeastern University in China. She has been involved in the research of the flotation of carbonate minerals. She has published over 6 technical papers in mineral processing engineering. Na Luo holds BS and MS degrees from Central South University in China.

De-zhou Wei a professor and doctoral supervisor of Northeastern University in China. He has also been a member of academic board of State Key Laboratory of Mineral Processing Science and Technology (Beijing General Research Institute of mining and metallurgy) and a director of China Gold Association. He receives a special government subsidy of the State Councial. His research areas are resources and environmental microbial technology, theory and technology of mineral processing. As the project leader, he has undertaken or completed 4 projects supported by the National Natural Science Foundation of China. Dr. Wei has published over 200 technical papers and 4 books including “Solid Material Selection” and “Application of Biotechnology in Mineral Processing”. Dr. Wei also holds BS, MS and Ph.D. degrees from Northeastern University in China.

Yan-bai Shen is a professor and doctoral supervisor of Northeastern University in China. He has also been a member of Japan Society of Applied Physics and Japan Society of catalysis. He has been involved in the research of inorganic non-metallic materials and its applications in sensors. Dr. Shen has published over 100 technical papers and 1 textbook which is “Metal Oxide Nanomaterial Gas Sensors”. Dr. Shen holds BS, MS degrees from Northeastern University in China and Ph.D. degree from Toyama University in Japan.

Wen-gang Liu is a professor and doctoral supervisor of Northeastern University in China. His main research interests are environmental protection in mineral processing and development of beneficiation reagents and separation theory. Dr. Liu has co-written 3 textbooks and published over 20 technical papers,the latest being “Synthesis of N, N-Bis (2-hydroxypropyl) laurylamine and its flotation on quartz” published in Chemical Engineering Journal in 309 Volume, 2017. He holds BS, MS and Ph.D. degrees from Northeastern University in China.

Shu-ling Gao is an associate professor of Northeastern University in China. Her main research interests are theory and technology of mineral processing, numerical simulation of flow field and process simulation. Dr. Gao has co-written 2 textbooks and published over 20 technical papers. In recent years, she has presided over or participated in more than 20 scientific research subjects, such as the National Natural Science Foundation of China Youth Foud, the national science and technology support program of China, national major projects of China. She got BS, MS degrees from China University of Mining and Technology and Ph.D. degree from Northeastern University in China.

Copyright © 2017. Brazilian Metallurgical, Materials and Mining Association
Journal of Materials Research and Technology

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