Recovery of Magnesium and Potassium from Biotite by Sulfuric Acid Leaching and Alkali Precipitation with Ammonia

Hydrometallurgy 157 (2015) 188–193

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Recovery of magnesium and potassium from biotite by sulfuric acid leaching and alkali precipitation with ammonia

Zheng Luo a,c,JingYanga,b,⁎,HongwenMaa,b,⁎, Meitang Liu a,XiMaa a School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China b Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, China University of Geosciences, Beijing 100083, China c Bluesky Technology Corporation, Beijing 100083, China article info abstract

Article history: A process for the recovery of magnesium (Mg) and potassium (K) from biotite was developed using sulfuric acid Received 24 February 2015 leaching and precipitation with ammonia. The optimum conditions for dissolution of biotite were found to be Received in revised form 19 August 2015 sulfuric acid solution of 2.5 mol/L, sulfuric acid/biotite ratio of 4 mL/g, leaching temperature of 90 °C and leaching Accepted 22 August 2015 time of 2 h. Under these conditions, the leaching efficiency of Mg and K was found to be 95.8% and 94.9% respec- Available online 29 August 2015 tively. By using the solubility differences of corresponding elements, a two-step precipitation process was applied to remove Fe and Al and recovery of Mg. Subsequently, magnesium hydroxide was prepared by precipitation Keywords: Biotite from the leach solution with ammonia as the precipitant. X-ray diffraction (XRD) and scanning electron micro- fl Magnesium hydroxide scope (SEM) analyses showed that the high purity Mg(OH)2 existed in the form of ower-like spherical aggrega- Ammonium–potassium sulfate tion. Furthermore, the final solution of ammonium–potassium sulfate can be used for agricultural compound Recovery fertilizer. © 2015 Elsevier B.V. All rights reserved.

1. Introduction solution with ammonia as the precipitant and sodium dodecyl sulfate as the modifier. Magnesium hydroxide is a popular inorganic compound because of In many studies, magnesium could be recovered from tailings and its wide range of applications. It plays an important role in many fields, waste residues. Ma et al. (2014a) treated boron mud with about 40% such as flame retardant in polymers, special ceramics, fillers in magnesia which is a potential magnesium source for synthesis of bleaching agent and a raw material for preparation of magnesium Mg(OH)2 and proposed the formation mechanism of the flower-like oxide (Sonawane et al., 2010; Pavlović et al., 2010; Liu et al., 2011). Mg(OH)2 via anti-drop precipitation method. In another study, Magnesium hydroxide can be prepared by several methods, such as Özdemir et al. (2009) used hydrochloric acid to recovery magnesium hydration of magnesium oxide, electrolysis of magnesium salt aqueous from magnesite tailings. MgCl2 ·6H2O with a purity of 91% was pro- solutions, sol–gel techniques and precipitation (Yu et al., 2004; duced by evaporation of leach solution obtained at 40 °C for 60 min, Utamapanya et al., 1991). Magnesium is found in many minerals such 1.0 M acid, solid-to-liquid ratio of 10 g/L. Karidakis et al. (2005) investi- as magnesite, dolomite, brucite, serpentinite (Tran et al., 2013). Elsner gated the recovery of magnesium from nickel laterite with sulphuric and Rothon (1998) extracted magnesium from a magnesite ore by acid leaching followed by precipitation with Ca(OH)2 and the precipi- leaching with HNO3. This was followed by purification at pH 5–6 using tate was a mixture of Mg(OH)2 and CaSO4 ·2H2O. The magnesium re- NH4OH and H2O2 and then precipitation to produce Mg(OH)2. Nduagu covery rate of 90–99% could be achieved at only 20 °C for the et al. (2012) processed a serpentinite ore containing 21.8% Mg to pre- precipitation. pare high purity Mg(OH)2. Mixtures of the ore with ammonium sulfate Potassium (K) is an essential element for plant nutrition and potas- at a mass ratio of 0.5–0.7 were roasted at 400–550 °C and Mg(OH)2 was sium salts are mainly produced by water soluble potassium resources. recovered at pH 10–11 using NH3 gas after purification. Xiong et al. However, China only possesses 210 million tons of the global potash re- (2014) extracted magnesium from dolomitic phosphate ore (7.67% serves which is totally 6 billion tons around the world (US Geological MgO) with dilute waste acid. Operating under the optimum leaching Survey, 2014) and imports several million tons of potash fertilizer conditions, a 98.31% recovery of Mg with 0.02% P2O5 loss was obtained. each year. Under such circumstances, the recovery of K from different Magnesium hydroxide was prepared by precipitation from the refined indigenous sources is highly essential in China. The N–K nutrient bal- ance was highly significant for dry matter yield and tiller development indicating that optimum yield was obtained only when both elements ⁎ Corresponding authors at: School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China. were adequately supplied (MacLeod, 1965; Grant and MacLean, E-mail addresses: [email protected] (J. Yang), [email protected] (H. Ma). 1966). Later studies by Opuwaribo and Odu (1978); Lumbanraja and

Evangelou (1990, 1992, 1994),andShen et al. (1997) reported that K+, + added simultaneously with NH4 , stimulated N2- fixation in soils containing illite, vermiculite and mica. In this context, some efforts have been made to recover potassium for obtaining soluble K from K-feldspar and biotite. Earlier in 1997, Varadachari developed a process for the production of potassium chloride from biotite. The kinetics of reaction of biotite with HCl was re- vealed that leaching of K+ from biotite followed first-order kinetics and the key process is the replacement of K+ by H+ in the interlayer space. After purification, KCl was recovered using ethanol (Varadachari, 1992, 1997). Jena et al. (2014) observed that the potassium values present in nepheline syenite (5.4% K2O) were unlocked through roasting with calcium chloride followed by water leaching. In this report, it is possible to recover ~99.6% K2O value by calcination at 900 °C for 30 min. Ma et al. (2014b) reported that K-feldspar was easily transformed into kalsilite by removing 2/3 SiO2 from the feldspar in the KOH-H2Osolution. Kalsilite was then decomposed with sulfuric acid and the nearly pure solution of potassium sulfate was obtained. During the process, the recovery ratio of K2O was up to 94.0%. Biotite (K(Mg,Fe)3AlSi3O10(OH)2) is a kind of layered aluminosili- cate mineral with some valuable elements of magnesium and potassium. Compared with other kinds of mica, like phlogopite and lepidolite, which are of practical importance in industry, biotite, containing iron inside, is greatly restrained from practical use due to its poor insulation performance. As a result, biotite slice could only be used as cheap fillings of building materials. In Qinghai province of Fig. 1. Flowchart diagram showing process for the recovery of Mg and K from biotite. China, 45,000 t of biotite as a by-product of phosphate ore, containing – ~20% MgO and 9 10% K2O were produced while processing 300,000 t of Φ5 mm steel balls. The milling was operated in the air with 50 g of of phosphate ore per year. Therefore, it attaches a great practical impor- mineral biotite per cell and a total of 200 g for 2 h. The average particle tance on researching how to recover Mg and K by using the biotite. Pre- size (d80) of biotite was 150 μm. liminary investigations indicated that metal cations in biotite can be The flowchart for Mg and K recovery from biotite by acid leaching easily dissolved by inorganic acid (HCl and H2SO4), and hydrochloric and alkali precipitation is shown in Fig. 1. The leaching experiments acid was founded to be the most effective in terms of rate of leaching ef- were performed in a glass 100-mL flask equipped with a magnetic stir- fi ciency (Varadachari, 1992, 1997). However, it is evident from the liter- rer with an agitation speed of 200 rpm and a reflux condenser to pre- ature that Cl can be toxic to some plants and higher than adequate rates vent evaporation loss, which was bathed in a water bath. Biotite (5 g) of K as KCl caused a yield reduction due to damage caused from an ex- was reacted with different concentrations of sulfuric acid (1.85–2.7 cess of Cl (Rominger et al., 1976). Therefore sulfuric acid was used to de- mol/L), with different sulfuric acid/biotite mass ratios (3:1–7:1 mL/g), stroy biotite in this research. different leaching times (0.5–2.5 h) and different leaching temperatures In this paper, an innovative process to recover magnesium and po- (25, 60, 70, 80 and 90 °C). After the acid leaching, the mixture was fil- tassium from the Qinghai biotite is proposed, which is suitable to deal tered through 0.5-μmporesizewhitefilter paper using a pressure filtra- with magnesium-rich biotite. It aims to optimize the conditions for tion unit and washed to separate the leached residue and the solution. magnesium and potassium recovery from biotite by leaching with sulfu- The Mg2+,K+,Fe2+,Fe3+,andAl3+ contents in the solutions were de- fi ric acid solution and to determine factors affecting its leaching ef cien- termined by wet chemical analysis. A measured amount of hydrogen cy. Various process parameters like the concentration of sulfuric acid, peroxide solution containing 30 wt.% H2O2 was added to the solution leaching time and temperature are investigated in terms of metal to oxidize Fe2+ to Fe3+ at room temperature for 30 min under stirring fi leaching ef ciency. Then, a two-step precipitation process was applied at 200 rpm. The acidic leaching solution was then adjusted to pH 8.0 to prepare Mg(OH)2 and recovery of potassium from the leach solution with ammonia to precipitate Al and Fe, and retain K and Mg in solution. using ammonia. Finally, the production of Mg(OH)2 was also determined by XRD and SEM methods.

2. Materials and methods

2.1. Materials

The biotite mineral sample, which was produced from a beneﬁcia- tion of phosphate ore, was from Shangzhuang county of Qinghai province (China). Sulfuric acid and ammonia used were of analytical reagent grade and all the solutions with speciﬁed concentrations were prepared with distilled water.

2.2. Experimental procedures

A planetary ball mill with a rotation speed of 200 rpm was employed for mechanical activation. Four milling cells were ﬁxed on its platform, and each cell was composed of a 500-mL stainless steel vessel ﬁlled with 250 g of 2B mm steel balls, 200 g of Φ10 mm steel balls and 50 g Fig. 2. XRD pattern of biotite mineral powder. 190 Z. Luo et al. / Hydrometallurgy 157 (2015) 188–193

Table 1 Chemical analysis of biotite mineral powder (wt.%).

SiO2 TiO2 Al2O3 Fe2O3 FeO MnO MgO CaO Na2OK2OP2O5 LOI Total 39.45 1.28 14.40 2.64 5.69 0.02 20.19 2.99 0.86 9.70 0.15 1.93 99.50

2+ 3+ Table 2 (K0.840Na0.009Ca0.001)(Mg2.365Fe 0.421Mn0.002Fe 0.063Al0.100Ti0.071) Microprobe analysis of the biotite sample (wt.%). [Al1.199Si2.801O10](OH)2.

SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2OK2OP2O5 Total The mole fraction of the end-member components in the biotite 38.02 1.29 14.96 7.85 0.03 21.54 0.01 0.06 8.94 0.02 92.70 powder was: phlogopite (phl), 0.611; annite (ann), 0.133; eastonite (east), 0.095; Ti-biotite (tbi), 0.067; Fe3+-biotite (fbi), 0.094.

Finally, a Mg(OH)2 precipitate was obtained by adjusting the pH to 11.0, 3.2. Reactions of biotite with H SO whereas the potassium/ammonium sulfate solution was achieved by fil- 2 4 tration using the pressure filtration unit. The precipitate was dried at The leaching experiments were investigated to determine the 105 °C for 24 h to obtain magnesium hydroxide. optimum leaching efficiency from the biotite. Theoretically, the leaching reactions of biotite with H SO solution can be represented as: 2.3. Characterization 2 4 ð Þ ð Þþ þ ¼ þ þ 2þ þ 3þ þ ð Þ KMg3AlSi3O10 OH 2 phl 10H K 3Mg Al 3H4SiO4 1 X-ray diffraction (XRD) patterns of the biotite powder and leached residues were recorded with a Rigaku D diffractometer operating in 2þ ð Þ ð Þþ þ ¼ þ þ 2þ þ 3þ þ ð Þ KFe3 AlSi3O10 OH 2 ann 10H K 3Fe Al 3H4SiO4 2 Bragg–Brentano geometry with CuKα radiation (40 kV and 40 mA) and secondary monochromation. Data collection was conducted in the ð Þ ð Þþ þ ¼ þ þ 2þ þ 3þ þ þ KAlMg2Al2Si2O10 OH 2 east 14H K 2Mg 3Al 2H4SiO4 4H2O 2θ range of 3 to 70°, with a step size of 0.02°. The chemical compositions ð3Þ of the prepared samples were determined by wet chemical analysis fl (Maxwell, 1968). The K2O content was determined using the ame pho- ð Þ ð Þþ þ ¼ þ þ 2þ þ 4þ þ 3þ þ KMg2TiAlSi3O10 O 2 tbi 12H K 2Mg Ti Al 3H4SiO4 tometric method, the MgO and Al2O3 contents were determined using ð4Þ an EDTA complexometric, and the Fe2O3 content was determined by spectrophotometry. A Jeol JXA-8100 Superprobe was used as a scanning 3þ ð Þ ð Þþ þ ¼ þ þ 2þ þ 3þ þ 3þ electron microscope (SEM) and for electron microprobe analysis KFe Mg2Al2Si2O10 OH 2 fbi 14H K 2Mg Fe 2Al þ þ : ð Þ (EMPA), to visualize the minerals surface and to make qualitative and 2H4SiO4 4H2O 5 quantitative analyses. The spot diameter of the probe was 5 μm, and the operating conditions were 15 kV and 20 nA. 3.2.1. Effect of leaching time fi 3. Results and discussions Fig. 3 illustrates the effect of the reaction time on the leaching ef - ciency of Mg and K at sulfuric acid concentration of 2.5 mol/L, 90 °C, fi 3.1. Analysis of raw material and sulfuric acid-to-biotite ratio of 4 mL/g. The leaching ef ciency of Mg and K into solution increases with adding leaching time. When the fi XRD pattern of biotite mineral powder is given in Fig. 2.Itisshown leaching time is 1 h, the leaching ef ciency of Mg and K is less than fi that the major crystalline phase existed in the sample is biotite (JCPDS 75%. While extending time to 1.5 h, the leaching ef ciency of Mg and K reached up to 86%, and more than 94% of Mg and K can be leached Card No. 10–0495), which contained 20.19% MgO and 9.7% K2Oby chemical analysis as shown in Table 1. out after 2 h. Also, Fig. 3 shows that the dissolution rates of Mg and K According to the results (Table 2) of the analysis, the biotite crystal are very close and reach an apparent steady-state within 2 h. By con- chemical formula was calculated as follows (White et al., 2014; trast, studies of biotite weathering have indicated that fast preferential Holland and Powell, 2006): release of K followed by near-stoichiometric release of framework ions

Fig. 3. Effects of leaching time on Mg and K dissolution from biotite. Fig. 4. Effects of sulfuric acid concentrations on the leaching of Mg and K from biotite. Z. Luo et al. / Hydrometallurgy 157 (2015) 188–193 191

Fig. 5. Effects of temperatures on the leaching of Mg and K from biotite. Fig. 7. Precipitation rate of major metal ions from leach solutions at different pH.

(Mg, Al, Fe and Si) (Malmström and Banwart, 1997; Samson et al., and sulfuric acid-to-biotite ratio of 4 mL/g. As expected, the leaching ef- 2005). It may be that the much higher temperature and sulfuric acid ﬁciency of Mg and K increases with raising temperatures and the concentration can quickly destroy biotite structure. Then Mg and K dis- leaching efﬁciency of Mg and K was up to 95.8% and 94.9% at 90 °C. play a congruent dissolution. However, the temperatures continue to rise is advantageous to the formation of jarosite because of the presence of Fe, which could lead to a

3.2.2. Effect of H2SO4 concentration poor leaching efficiency of K (Wang et al., 2005; Baron and Palmer, The effect of acid concentrations on the leaching of Mg and K from 2002). In addition, Al may also incorporate into the leached residue as the biotite was examined using sulfuric acid-to-biotite ratio of 4 mL/g a result of precipitation of alunite and therefore causes a fallen in the at 90 °C for 2 h and the results are shown in Fig. 4. It can be seen that purity of silica gel (Liu and Papangelakis, 2005). Thus, the optimized the acid concentration has a significant impact on the leaching efficien- condition of the leaching temperature is 90 °C. cy of Mg and K, whose leaching efficiency was raised from 76 to 95% and

74 to 94% when the acid concentration of H2SO4 was varied from 1.85 mol/L to 2.5 mol/L respectively. The increase of magnesium and po- 3.2.4. Effect of sulfuric acid to biotite ratio tassium leaching efficiency while increasing the acid concentration is ItcanbeseeninFig. 6 that the leaching efficiency of Mg and K from due to acid concentration effect on increasing the H+ activity that biotite increased with an increase in sulfuric acid concentration to bio- results in further dissolution of biotite (Harvie et al., 1984). The leaching tite ration. When the sulfuric acid-to-biotite ratio was 4 mL/g, more efficiency reached the maximum value at the acid concentration of than 94% of Mg and K are leached. However, less than 90% of Mg and 2.5 mol/L. The reason for this may be due to the biotite structure K are leached out under a lower sulfuric acid-to-biotite ratio (3 mL/g). collapsing at this concentration or Mg2+ and K+ species block H+ diffu- When the sulfuric acid-to-biotite ratio is from 5 mL/g to 7 mL/g, the sion. Similar behavior was also observed in other studies (Özdemir and leaching efficiency changed a little compared to the result of 4 mL/g. Çetişli, 2005; Özdemir et al., 2009). This can be explained by the fact that the amount of solvent in the me- dium is sufficient to leach magnesium and potassium from biotite when 3.2.3. Effect of leaching temperature sulfuric acid-to-biotite ratio is high (Özdemir et al., 2009). Therefore, the Fig. 5 shows the effect of reaction temperatures on the leaching effi- optimized ratio of the sulfuric acid-to-biotite is 4 mL/g and it is favorable ciency of Mg and K at sulfuric acid concentration of 2.5 mol/L, time of 2 h for further recovery process.

Fig. 6. Effects of sulfuric acid/biotite ratios on the leaching of Mg and K from biotite. Fig. 8. XRD pattern of the synthesized Mg(OH)2 sample. 192 Z. Luo et al. / Hydrometallurgy 157 (2015) 188–193

Table 4 The mole concentration of the main components before and after two-step precipitation (mol/L).

Components K2SO4 Fe2(SO4)3 Al2(SO4)3 MgSO4 (NH4)2SO4 Acid leach solution 0.24 0.13 0.33 0.42 – Mother solution 0.24 ≤0.1 ≤0.1 ≤0.1 2.47

recovery of Mg in the second step of precipitation reached 99.9% Mg at pH 11.0.

3.4. Recovery of Mg and K

Mg(OH)2 was prepared by precipitation from the previous reﬁned leach solutions with ammonia as the precipitation agent. XRD pattern

of the Mg(OH)2 product was shown in Fig. 8. Seven peaks shown in the ﬁgure are consistent with the JPCDS Card No. 44–1482, indicating

that the synthesized Mg(OH)2 sample is of high purity. By the SEM image shown in Fig. 9,theﬂower-like Mg(OH)2 product was obtained, Fig. 9. SEM image of the synthesized Mg(OH)2 sample. which existed in the form of irregular spherical aggregation. It can be

seen in Table 3 that Mg(OH)2 was produced in a purity of 96% by the 3.3. Effect of pH on precipitation of metals from leach solution two-step precipitation process under these working conditions. In addition, the leached residue consisted mainly of 70.99% SiO2,1.17%Al2O3, The chemical reactions for metal ions with ammonia are as follows: 1.78% MgO and 20.79% weight loss and this can be used in glass, ceram- ic, and cement industries.

þ − After Mg(OH)2 precipitated, the ﬁnal solution is mainly composed of NH3 þ H2O ⇌ NH4 þ OH ð6Þ ammonium–potassium sulfate as shown in Table 4 which could be used 3þ þ − ¼ ð Þ ↓ ð Þ for agricultural compound fertilizer. Or, by separating K2SO4 and Fe 3OH Fe OH 3 7 (NH4)2SO4, the solution can be also used to prepare the agricultural potassium sulfate products while recovery of ammonia and sulfuric 3þ þ − ¼ ð Þ ↓ ð Þ Al 3OH Al OH 3 8 acid at 350 °C and 700 °C, respectively (Zhang, 2009).

Mg2þ þ 2OH− ¼ MgðOHÞ ↓: ð9Þ 2 4. Conclusions

2+ 3+ 3+ + The concentrations of metal ions (Mg ,Fe ,Al and K )deter- An innovative process for recovery of magnesium hydroxide as well mined were then used to characterize the precipitation rate as a func- as ammonium–potassium sulfate from a magnesium-rich biotite was tion of pH. The precipitation rate of the ion was calculated as follows: developed by sulfuric acid leaching and alkali precipitation with ammonia. The experimental results showed that the H SO concentration of C 2 4 Ion precipitation rate ðÞ¼% 1− i 100% ð10Þ 2.5 mol/L, sulfuric acid–biotite ratio of 4 mL/g, leaching temperature of C 0 90 °C and leaching time of 2 h resulted in high leaching efficiencies of Mg (95.8%) and K (94.9%). Purified Mg(OH) sample with flower-like fi 2 where C0 and Ci are the concentrations of the speci c element in morphology was achieved successfully with a two-step precipitation ac- initial and titrated leachate solution. cording to the various precipitation rates of the major metal ions by 2+ 3+ 2+ Fig. 7 presents the precipitation rate of Mg ,Fe (Fe has been using ammonia as the precipitant. Al and Fe ions were removed at 3+ oxidized by hydrogen peroxide treatment)and Al from leach solu- pH 8 and most of the Mg ions precipitated at pH 11.0. In addition to 3+ 3+ tions as a function of pH. Most of Fe and Al precipitate when the this, agricultural ammonium–potassium sulfate as the raw materials 2+ pH value is 8 whereas about 10% of Mg precipitates. The precipitation of fertilizer had been obtained as well. Therefore, the profitability of 2+ rate of Mg begins to increase with the pH value ranging from 8.0 to this process will be considerably high and this study will be valuable. 11.0. Therefore, according to the different precipitation rate between Mg2+ and the other two metal ions, a two-step precipitation process with the neutralizing agent was adopted. Fe and Al removal increased Acknowledgments by adding the pH, whereas the magnesium loss increased distinctly at pH N 8.0. Consequently, the optimum pH value at the first step for Fe, The authors gratefully acknowledge the support of Fundamental Al ions and Mg ion separation is about 8.0, at which the majority of Research Funds for the Central Universities (2652014017), China 3+ 3+ Fe ,Al have been precipitated as Fe(OH)3 and Al(OH)3 mixture Geological Survey Project (12120113087700), and the National Key which could be used to prepare ferric oxide, aluminum hydroxide Technology R&D Program in the 11th five-year plan of China separately, while near 10% of magnesium is in the solid residual. The (2006BAD10B04).

Table 3 Chemical analysis of residues (wt.%).

Components SiO2 TiO2 Al2O3 FeO total MnO MgO CaO Na2OK2OP2O5 LOI Total Silica gel 70.99 0.15 1.17 0.97 0.01 1.78 3.11 0.00 0.50 0.01 20.79 99.49 hydroxides of Al and Fe 1.04 0.74 24.98 15.62 0.01 2.07 0.84 0.00 0.62 0.05 53.41 99.38

Mg(OH)2 precipitate 0.83 0.01 0.56 0.19 0.00 66.27 0.40 0.00 0.16 0.00 31.08 99.50 Z. Luo et al. / Hydrometallurgy 157 (2015) 188–193 193

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