Trans. Nonferrous Met. Soc. China 27(2017) 908-916

Effects of iron-containing phases on transformation of sulfur-bearing ions in sodium aluminate solution

Xiao-bin LI, Fei NIU, Gui-hua LIU, Tian-gui QI, Qiu-sheng ZHOU, Zhi-hong PENG

School of Metallurgy and Environment, Central South University, Changsha 410083, China

Received 20 May 2016; accepted 23 November 2016

Abstract: Sulfides in the high-sulfur bauxite lead to serious steel equipment corrosion and alumina product degradation via the Bayer process, owing to the reactions of sulfur and iron-containing phases in the sodium aluminate solution. The effects of iron-containing phases on the transformation of sulfur-bearing ions (S^2-, ,  and ) in sodium aluminate solution were investigated. Fe, Fe₂O₃ and Fe₃O₄ barely react with and , but all of them, particularly Fe, can promote the conversion of  to  and S^2- in sodium aluminate solution. Fe can convert to  in solution at elevated temperatures, and further react with S^2- to form FeS₂, but Fe₂O₃ and Fe₃O₄ have little influence on the reaction behavior of S^2- in sodium aluminate solution. Increasing temperature, duration, dosage of Fe, mole ratio of Na₂O_k to Al₂O₃ and caustic soda concentration are beneficial to the transformation of  to  and S^2-. The results may contribute to the development of technologies for alleviating the equipment corrosion and reducing caustic consumption during the high-sulfur bauxite treatment by the Bayer process.

Key words: high-sulfur bauxite; sodium aluminate solution; sulfur-bearing ion; iron-containing phase; transformation

1 Introduction

More than 560 million tons of high-sulfur diasporic bauxite resources have not been effectively utilized in China [1,2]. The main sulfide mineral in the bauxite is pyrite (FeS₂) which readily reacts with alkaline solution in the Bayer process, resulting in the increase of caustic consumption, serious equipment corrosion, and Fe-contamination of alumina product [2-4]. In order to resolve such problems, many scholars have conducted researches which focused on: 1) pyrite removal from bauxite by pretreatments, such as roasting [4], flotation [5], and bio-beneficiation [6]; 2) removal of S^2- from Bayer liquor, such as through formation of ZnS by adding Zn(II) [3,7] or NaFeS₂·2H₂O by adding fresh iron hydroxides [8]; 3) removal of  from Bayer liquor through formation of BaSO₄ by adding barium compounds [9]; 4) conversion of S^2- to  during the Bayer digestion process by addition of oxidants, such as O₂ [10,11] and NaNO₃ [12]. However, inefficient desulfurization, high cost and complicated operation limit the practical application of these methods. Therefore, developing new methods to minimize the impact of sulfur-containing minerals is crucial for utilization of high-sulfur bauxite.

During the Bayer digestion process, sulfur- containing minerals in bauxite inevitably react with the alkaline solution to form S^2-, ,  and  etc., and these sulfur-bearing ions would further react with Fe (in steel equipment), Fe₂O₃ or Fe₃O₄ (in bauxite). The adverse effects of sulfur-containing species on the alumina production process are generally believed to be caused by these various reactions. KUZNETSOV et al [13] and LI et al [14] investigated the reactions of FeS₂ in sodium aluminate solution at elevated temperatures, and proposed that the soluble iron-sulfur complex generated by sulfur and iron-containing phases was the main reason for Fe-contamination of the product. XIE  et al [15-17] studied the influence of S^2- on corrosion of steels in sodium aluminate solution and suggested that S^2- could react with steel to generate iron-sulfur compounds with loose structure and thus accelerate the corrosion. XIE et al [16] also reported that the corrosion of steels could be decelerated by  anion in sodium aluminate solution, while WENSLEY and CHARLTON [18] found that both S^2- and  anions were the corrosion activators for steels in alkaline solution. Compared with the low-valence sulfur ions,  and  were believed to be harmless to the corrosion of steel equipment and Fe-contamination of alumina products.

In view of different impacts of various sulfur- bearing ions, the conversions of sulfur-bearing ions in aluminate solution have received considerable research attention. ABIKENOVA et al [19], and HU and CHEN [10] investigated the transformation of S^2- in sodium aluminate solution in the presence of oxidants, and demonstrated that the transformation process among sulfur-bearing ions, i.e., S^2- was first oxidized to  and then to  or  which was finally converted to . However, the conversion behaviors of sulfur-bearing ions during the reactions of them with iron-bearing substances were not taken into consideration.

In sum, understanding the reaction behaviors of the iron-containing phases and the sulfur-bearing ions as well as the transformation of the sulfur-bearing ions is essential to develop new technologies for high-sulfur bauxite utilization. Unfortunately, the previous researches paid much attention to the transformation of iron-bearing species in the sulfur-containing solutions, while the effects of iron-containing phases on transformation of the sulfur-bearing ions have been scarcely reported. In view of this, this work focused on the dependence of sulfur-bearing ion (S^2-, ,  and ) transformation on iron-containing phases (Fe, Fe₂O₃ and Fe₃O₄) in sodium aluminate solution. We attempted to provide the fundamental basis for taking some measures to reduce the steel equipment corrosion, caustic soda loss and the product Fe-contamination during the high-sulfur bauxite treatment by the Bayer process.

2 Experimental

2.1 Materials

Sodium aluminate solutions were prepared by dissolving industrial grade aluminum hydroxide (Aluminum Corporation of China) into hot sodium hydroxide solution. Various sulfur-bearing ion solutions were obtained by adding analytical grade of Na₂S·9H₂O (Xilong Chemical Co., Ltd.), Na₂S₂O₃·5H₂O, Na₂SO₃ or Na₂SO₄ (Sinopharm Chemical Reagent Co., Ltd.) of a defined dosage into the prepared sodium aluminate solution. Both iron powder (Kermel Chemical Reagent Corporation of Tianjing, China) and Fe₂O₃ powder (Sinopharm Chemical Reagent Co., Ltd.) were analytical grade reagents, Fe₃O₄ powder (Sinopharm Chemical Reagent Co., Ltd.) was chemically pure reagent, and no other phases were detected in these iron-containing phases (Fig. 1).

Fig. 1 XRD patterns of iron-containing phases

2.2 Methodology

The digestion experiments were performed in a self-designed autoclave, in which the sealed stainless bombs (150 mL) were heated in either molten salts (>160 °C) or glycerol (<140 °C). A given mass of iron-containing substance and 100 mL sulfur-bearing sodium aluminate solution were added into a 150 mL bomb, together with four steel balls (two 18 mm- diameter and two 8 mm-diameter) for improved agitation. The sealed bomb was fixed in a rotating device (rotation speed of 120 r/min), immersed in the heating medium and was retained for fixed duration at the designated temperature. The resultant slurry obtained was filtered and washed using hot water. The filtrate was collected for sulfur-bearing ions analysis, and the residue was dried at (50±1) °C for 24 h.

The sodium aluminate solutions were characterized by Na₂O_k concentration and caustic molar ratio (α_k). The Na₂O_k represents caustic soda as Na₂O in solution, and the α_k refers to the molar ratio of Na₂O_k to Al₂O₃. The concentrations of Na₂O_k and Al₂O₃ were determined by titration [20]. The concentrations of sulfur-bearing ions were characterized by the mass concentration of element sulfur, and the total sulfur concentration (S_T) is the summation of concentrations of S^2-, ,  and  in solution. The concentrations of ,  and  were simultaneously analyzed by an ion chromatograph (ICS-90, Dionex, USA) and designated respectively as x₂, x₃ and x₄. The total concentration (x) of S^2-,  and  was measured by titration [21]. Hence, the S^2- concentration (x₁) can be calculated by subtraction, i.e., x₁=x-x₂-x₃. Every digestion experiment was conducted at least twice to verify the variation of the sulfur-bearing ions, average concentrations of sulfur-bearing ions were recorded. X-ray diffraction (D/MAAX2500, Rigaku Corporation, Japan) was applied to characterizing the residues using Cu K_α radiation at a scanning speed of 8 (°)/min. The contents of sodium and sulfur in residues were identified by flame photometer (AP1302, Shanghai Aopu Analytical Instruments Corporation, China) and sulfur analyzer (HDS3000, Hunan Huade Electronics Corporation, China), respectively.

3 Results and discussion

3.1 Effects of iron-containing phases on reaction behavior of sulfur-bearing ions

The digestion of diasporic bauxite was generally conducted at 260-280 °C with the Na₂O_k concentration of about 230 g/L and α_k of 3.0 in the alumina refineries. The main iron-containing phases involved in the digestion process were Fe (steel equipment) and iron oxides (main iron minerals in bauxite and the passivation coating of the steel equipment). In order to reveal the effects of iron-containing phases (Fe, Fe₂O₃ and Fe₃O₄) on the transformation of sulfur-bearing ions, the concentration variation of sulfur-bearing ions was investigated in sodium aluminate solution during the digestion process with adding various iron-bearing phases. Blank experiments without the addition of the iron-containing phases were also conducted for comparison. Moreover, in order to react with the sulfur-bearing ions adequately during the digestion, and the initial dosage of iron-containing phases was determined with the mole ratio of Fe to S being 1.5:1.

3.1.1 Effects of iron-containing phases on reaction behavior of S^2-

When high-sulfur bauxite is treated using the Bayer process, the sulfur exists in solution predominately in the form of S^2-. The influence of iron-containing phases on the transformation of S^2- is shown in Table 1.  and  were detected in the starting solution prepared by dissolving Na₂S·9H₂O, which may be contributed to the oxidation of S^2- during the preparation.

Table 1 shows that the S^2- concentration is reduced by varying degrees after digestion with adding different iron-containing phases, and the sulfur concentration in residues is increased. When adding iron, Fe₃O₄ or Fe₂O₃ powders, the concentrations of S^2- in the digested solutions correspondingly decrease by 17.33%, 6.56% and 3.28% compared with the concentration of S^2- in the blank digested solution. The S^2- concentration in the blank digested solution decreases slightly along with a small increase of concentrations of  and  compared with the starting solution, which may be caused by the oxidation of S^2- during the digestion. The result shows that S^2- concentration decreases obviously on addition of the iron-containing phases in digestion process accompanying by an increase in  and  concentrations. Table 1 also reveals that the S^2- concentration variation is related to the valence of iron, i.e., the iron with the smallest valence favors the most decreased S^2- concentration in the digested solution.

3.1.2 Effects of iron-containing phases on reaction behavior of

The pyrite in bauxite will react with alkaline solution forming S^2- and  firstly in the Bayer digestion process. The S^2- ion can be oxidized into  and other high valence sulfur-bearing ions in sodium aluminate solution during the alumina production [19]. was found to accelerate the equipment corrosion [22]. The effects of iron-containing phases on the transformation of  in sodium aluminate solution were also studied. The results are shown in Table 2.

As shown in Table 2, the concentration of decreases significantly in sodium aluminate solution after digestion. Compared with the starting solution, about 75% of  transforms to  and S^2- in the blank sample, possibly due to the disproportionation reaction of . The transformations of  are enhanced by differing degrees on addition of the iron-containing phases. Besides,  can completely convert into  and S^2- on addition of iron powder, suggesting that the transformation of  can be accelerated obviously by iron powder, and the possible reactions can be proposed as Eqs. (1) and (2) [23].

Fe += FeS+                          (1)

FeS+3OH^-=+S^2-                               (2)

In addition, the formed FeS may further react with OH^- in sodium aluminate solution during the digestion process at elevated temperature (Eq. (2)), resulting in the increase of  and S^2- concentrations in digested solution.

3.1.3 Effects of iron-containing phases on transformation of  or

In general, S^2- can be oxidized to  and  by O₂ or other oxidants [3,12] in the Bayer process. The effects of iron-containing phases on the transformation of  and  were concerned in sodium aluminate solution, and the results are presented in Tables 3 and 4, respectively.

Table 3 indicates that  concentration has no remarkable variation and  is present in solution for all experiments. The presence of  can be attributed to the oxidation of  in sample preparation or the impurity of  in Na₂SO₃. In comparison with the other samples, the lower  concentration with adding iron powder may be caused by the inhibition of oxidation. The results in Table 4 demonstrate that iron-containing phases have no evident influence on the transformation of  in sodium aluminate solution. Moreover, the sulfur contents in residues approximate to zero, and neither  nor  appears to react with iron-containing phases during the Bayer digestion process of diasporic bauxite, which is in agreement with previous research [18].

Table 1 Effects of iron-containing phases on reaction behavior of S^2- in sodium aluminate solution

Table 2 Effects of iron-containing phases on transformation of in sodium aluminate solution

Table 3 Effects of iron-containing phases on transformation of  in sodium aluminate solution

Table 4 Effects of iron-containing phases on the transformation of  in sodium aluminate solution

3.1.4 Phase analysis of residues obtained from reaction of iron-containing phases with S^2- or

As discussed above, both S^2- and  in sodium aluminate solution can react with the iron-containing phases. For better understanding the reaction mechanism, the XRD analysis of residues generated by the reaction of iron-containing phases with S^2- and  was conducted, and the results are displayed in Fig. 2.

Fig. 2 XRD patterns of residues produced by reaction of iron-containing phases with S^2- (a) and  (b)

No new phases are detected using XRD analysis in the residues obtained by adding Fe₂O₃ or Fe₃O₄, which suggests that either Fe₂O₃ or Fe₃O₄ has little influence on the transformation of S^2- or  in sodium aluminate solution, being consistent with the results in Tables 1 and 2. Whereas, evident characteristic peaks of Fe₃O₄ and faint characteristic peak (at about 2θ=16.5°) appear in the XRD patterns of the residues obtained by adding iron powder. The possible phase at 2θ=16.5° may be FeS₂ or NaFeS₂·2H₂O [8], which can be formed by the ferrous or ferric compound reacting with S^2- in sodium aluminate solution, respectively. The contents of sodium and sulfur were detected (in Table 5) to identify the phases in residues. In view of the low sodium contents and high sulfur contents in residues, the formation of FeS₂ at 2θ=16.5° can be verified.

Table 5 Contents of sodium and sulfur in residues

According to the previous studies [24-26], iron can convert to  and Fe₃O₄ in alkaline solution at elevated temperatures.  may react with S^2- to form FeS₂ in sodium aluminate solution during the temperature decrease process after digestion, as discussed by LI et al [8], leading to decreased S^2- concentration (Table 1). On addition of Fe₂O₃ and Fe₃O₄ powders, little  is formed in the solution. Therefore, iron powder promotes the transformation of S^2- into residues more greatly than Fe₂O₃ or Fe₃O₄ powders. It is comprehensible that iron powders can enhance the conversion of  to  and S^2-, and S^2- then partly incorporates in FeS₂, reducing  concentration and increasing  concentration (in Table 2).

3.2 Effects of duration and iron powder dosage on transformation of S^2- and

The influences of duration and iron powder dosage on the transformation of S^2- and  at different temperatures are presented in Figs. 3-5, respectively.

Figure 3(a) indicates that the main sulfur-bearing ion is S^2- in solution, coexisting a small amount of  and . The concentrations of S_T, ,  and S^2- in solution remain almost unchanged at 80 °C as a function of duration, suggesting that S^2- reacts weakly with iron powder in sodium aluminate solution at low temperatures. However, when the reaction temperature is increased to 260 °C (Fig. 3(b)), the concentration of S^2- decreases slightly with the duration prolonging. The S^2- concentration decreases from 4.05 to 3.52 g/L in 10 min, and then reaches 3.27 g/L at 90 min. The concentration increases slightly and  concentration remains almost constant, i.e.,  is difficult to convert to .

concentration decreases and  concentration increases with duration at either 120 or 260 °C (Fig. 4). Increasing temperature favors the conversion, e.g.,  concentration reduces to zero in 10 min at 260 °C along with marked increase in  concentration and slight raising of S^2- concentration instead of being proportional to  concentration, where the S_T concentration reduces from 5.28 to 4.17 g/L. The obvious reduction of S_T concentration and the inconspicuous variation of S^2- concentration are caused by the formation of FeS₂.

The iron powder dosage has a significant influence on reducing the S^2- concentration until 8.75 g/L (mole ratio of Fe to S being ~1), further increase in iron powder dosage does not result in further reduction of S^2- concentration (Fig. 5(a)). The variation of  concentration shows a similar trend with the effect of iron powder dosage, the critical dosage is about 4.38 g/L (mole ratio of Fe to S being ~0.5) (Fig. 5(b)). The variation tendencies of other sulfur-bearing ions with increasing the iron powder dosage in Figs. 5(a) and (b), including ,  and S^2-, are coincident with the results in Figs. 3(b) and 4(b), respectively.

Fig. 3 Effects of duration on reaction behavior of S^2- in sodium aluminate solution at 80 °C (a) and 260 °C (b)

Fig. 4 Effects of duration on reaction behavior of  in sodium aluminate solution at 120 °C (a) and 260 °C (b)

Fig. 5 Effects of iron powder dosage on reaction of S^2- (a) and  (b) in sodium aluminate solution

3.3 Effects of α_k and Na₂O_k concentration on transformation of S^2- and

As α_k and Na₂O_k concentration are important characteristics of the sodium aluminate solution and vary in the Bayer process, their influences on the transformation of S^2- and  were determined experimentally. The compositions of starting sodium aluminate solutions are listed in Table 6, and the results of the effect of α_k and Na₂O_k concentration are presented in Figs. 6 and 7, respectively.

Table 6 Compositions of starting sodium aluminate solutions

Fig. 6 Effects of α_k on reaction of S^2- (a) and  (b) in sodium aluminate solution

The S^2- concentration reduces with increasing α_k, while the S_T in solution initially decreases and then remains stable (Fig. 6(a)). Figure 6(b) shows that the  concentration also decreases with increasing α_k, and that  can even completely convert to  and S^2- in solution at α_k greater than 2.07.

Fig. 7 Effects of Na₂O_k concentration on reaction of S^2- (a) and  (b) in sodium aluminate solution

It is also demonstrated that higher Na₂O_k concentration can expedite the reaction of S^2- with iron powder (Fig. 7(a)) with the Na₂O_k concentration ranging from 170 to 300 g/L,  can be completely transformed and its concentration declines to zero (Fig. 7(b)).

In summary, higher α_k or concentrated Na₂O_k, corresponding to greater free sodium hydroxide concentration, is conducive to the reaction of S^2- and  with iron powder due to increased formation of  [26]. In addition, the variations of  and  concentrations with α_k or Na₂O_k concentration exhibit the similar tendency to those with the increasing duration discussed in section 3.2.

4 Conclusions

1) Fe promotes the transformation of S^2- into residues, nevertheless, Fe₂O₃ and Fe₃O₄ have minimal effects on the reaction of S^2- at 260 °C. The iron- containing phases including Fe, Fe₂O₃ and Fe₃O₄, can promote  transformation to  and S^2-, but have little influences on the transformation of  and  in sodium aluminate solution.

2) The  formed by iron powder at elevated temperatures may react with S^2- in sodium aluminate to generate FeS₂ after digestion, resulting in the S^2- concentration decrease in solution.

3) Increasing the temperature, duration, dosage of iron powder, α_k and Na₂O_k concentration accelerates the transformation of S^2- and  in solution in the presence of iron powder.

References

[1] FU Shi-wei. Prospection analysis of development of high-sulfur bauxite of Guizhou [J]. Mineral Exploration, 2011(2): 159-164. (in Chinese)

[2] YIN Jian-guo, XIA Wen-tang, HAN Ming-rong. Resource utilization of high-sulfur bauxite of low-median grade in Chongqing, China [C]//Light Metals. San Diego, California: Wiley, 2011: 19-22.

[3] PENG Xin, JIN Li-ye. Development and application of bauxite containing high sulfur [J]. Light Metals, 2010(11): 14-17. (in Chinese)

[4] HU Xiao-lian, CHEN Wen-mi, XIE Qiao-ling. Sulfur phase and sulfur removal in high sulfur-containing bauxite [J]. Transactions of Nonferrous Metals Society of China, 2011, 21(7): 1641-1647.

[5] WANG Xiao-min, ZHANG Ting-an, Guo-zhi, BAO Li. Selection of flotation desulfurization collector for high-sulfur bauxite [J]. Journal of Northeastern University (Natural Science), 2010, 31(4): 555-558. (in Chinese)

[6] ZHOU Ji-kui, LI Hua-xia. Experimental research on bacterial oxidation of pyrite in high sulfur bauxite [J]. Metal Mine, 2011(12): 67-69. (in Chinese)

[7] LEWIS A E. Review of metal sulphide precipitation [J]. Hydrometallurgy, 2010, 104(2): 222-234.

[8] LI Xiao-bin, LI Chong-yang, PENG Zhi-hong, LIU Gui-hua, ZHOU Qiu-sheng, QI Tian-gui. Interaction of sulfur with iron-containing substances in sodium aluminate solutions [J]. Transactions of Nonferrous Metals Society of China, 2015, 25(2): 608-614.

[9] HE Run-de, TIAN Zhong-liang. Discussion on reasonable cost of sulphur removal with barium aluminate from industrial sodium aluminate solution [J]. Journal of Guizhou University of Technology (Natural Science Edition), 2000, 29(6): 54-58. (in Chinese)

[10] HU Xiao-lian, CHEN Wen-mi. Desulfurization from sodium aluminate solution by wet oxidation [J]. Journal of Central South University (Science and Technology), 2011, 42(10): 2911-2916. (in Chinese)

[11] LIU Zhan-wei, LI Wang-xing, MA Wen-hui, YIN Zhong-lin, WU Guo-bao. Conversion of sulfur by wet oxidation in the Bayer process [J]. Metallurgical and Materials Transactions B, 2015, 46(4): 1702-1708.

[12] LIU Zhan-wei, LI Wang-xing, MA Wen-hui, YIN Zhong-lin, WU Guo-bao. Comparison of deep desulfurization methods in alumina production process [J]. Journal of Central South University, 2015, 22(10): 3745-3750.

[13] KUZNETSOV S I, GRACHEV V V, TYURIN N G. Interaction of iron and sulfur in alkaline aluminate solutions [J]. Russian Journal of Applied Chemistry, 1975, 48(4): 748-750.

[14] LI Xiao-bin, LI Chong-yang, QI Tian-gui, ZHOU Qiu-sheng, LIU Gui-hua, PENG Zhi-hong. Reaction behavior of pyrite during Bayer digestion at high temperature [J]. The Chinese Journal of Nonferrous Metals, 2013, 23(3): 829-835. (in Chinese)

[15] XIE Qiao-ling, CHEN Wen-mi. Corrosion behavior of 16Mn low alloy steel in sulfide-containing Bayer solutions [J]. Corrosion Science, 2014, 86: 252-260.

[16] XIE Q L, CHEN W M, YANG Q. Influence of sulfur ions on corrosion of 16Mn low-alloy steel in sulfide-containing Bayer solutions [J]. Corrosion, 2014, 70(8): 842-849.

[17] XIE Qiao-ling, CHEN Wen-mi. Effect of S^2- on corrosion behavior of low alloy steel in sodium aluminate solution [J]. The Chinese Journal of Nonferrous Metals, 2013, 23(12): 3462-3469. (in Chinese)

[18] WENSLEY D A, CHARLTON R S. Corrosion studies in kraft white liquor potentiostatic polarization of mild steel in alkaline solutions containing sulfur species [J]. Corrosion, 1980, 36(8): 385-389.

[19] ABIKENOVA G K, KOVZALENKO V A, AMBARNIKOVA G A, IBRAGIMOVA A T. Investigation of the effect and behavior of sulfur compounds on the technological cycle of alumina production [J]. Russian Journal of Non-Ferrous Metals, 2008, 49(2): 91-96.

[20] WATTS H, UTLEY W. Volumetric analysis of sodium aluminate solutions [J]. Analytical Chemistry, 1953, 25(6): 864-867.

[21] CHEN Wen-mi, HU Qin. Research on the analysis of low-valence sulphion in sodium aluminate solution [J]. Light Metals, 2012(10): 17-20. (in Chinese)

[22] CHEN Wan-kun, PENG Guan-cai. The intensifying digestion of diasporic bauxite [M]. Beijing: Metallurgical Industry Press, 1997: 112-116. (in Chinese)

[23] VASQUEZ MOLL D V, SALVAREZZA R C, VIDELA H A, ARVIA A J. A comparative pitting corrosion study of mild steel in different alkaline solutions containing salts with sulphur-containing anions [J]. Corrosion Science, 1984, 24(9): 751-767.

[24] TREMAINE P R, LEBLANC J C. The solubility of magnetite and the hydrolysis and oxidation of Fe²⁺ in water to 300 °C [J]. Journal of Solution Chemistry, 1980, 9(6): 415-442.

[25] UCHIDA S, KASHIWAGI H, SATO T, OKUWAKI A. Formation of iron oxides by the oxidation of iron in Fe-MOH-H₂O and Fe-MOH-H₂O-O₂ systems (M=Li, Na, K) [J]. Journal of Materials Science, 1996, 31(14): 3827-3830.

[26] LI Xiao-bin, LIU Nan, QI Tian-gui, WANG Yi-lin, ZHOU Qiu-sheng, PENG Zhi-hong, LIU Gui-hua. Conversion of ferric oxide to magnetite by hydrothermal reduction in Bayer digestion process [J]. Transactions of Nonferrous Metals Society of China, 2015, 25(12): 3467-3474.

含铁物质对含硫离子在铝酸钠溶液中转化的影响

李小斌，牛 飞，刘桂华，齐天贵，周秋生，彭志宏

中南大学 冶金与环境学院，长沙 410083

摘  要：用拜耳法处理高硫铝土矿时，矿石中的硫化物会与含铁物质在铝酸钠溶液中反应，进而导致严重的设备腐蚀和氧化铝产品降级。本文作者研究含铁物质对含硫离子(S^2-，，和)在铝酸钠溶液中转化的影响。研究结果表明：铁粉、Fe₂O₃和Fe₃O₄均难以与和反应，而且所有含铁物质，特别是铁粉，均能促进转化为和S^2-；在高温条件下铁粉与铝酸钠溶液反应生成，进而可与S^2-反应生成FeS₂，但Fe₂O₃和Fe₃O₄对S^2-的反应影响很小；升高温度、延长反应时间、增加铁粉添加量、提高溶液中Na₂O_k与Al₂O₃的摩尔比和苛碱浓度均有利于向和S^2-转化。本研究结果有助于在拜耳法处理高硫铝土矿过程中开发减缓设备腐蚀和降低碱耗的技术。

关键词：高硫铝土矿；铝酸钠溶液；含硫离子；含铁物质；转化

(Edited by Wei-ping CHEN)

Foundation item: Project (51604309) supported by the National Natural Science Foundation of China; Project (201509048) supported by the Environmental Protection’s Special Scientific Research for Chinese Public Welfare Industry; Project (2015CX001) supported by the Innovation-driven Plan in Central South University, China

Corresponding author: Tian-gui QI; Tel/Fax: +86-731-88830453; E-mail: qitiangui@csu.edu.cn

DOI: 10.1016/S1003-6326(17)60105-5