• International Journal of Technology (IJTech)
  • Vol 11, No 4 (2020)

Sulfuric Acid Leaching of Heavy Rare Earth Elements (HREEs) from Indonesian Zircon Tailing

Iga Trisnawati, Gyan Prameswara, Panut Mulyono, Agus Prasetya, Himawan Tri Bayu Murti Petrus

Corresponding email: bayupetrus@ugm.ac.id

Cite this article as:
Trisnawati, I., Prameswara, G., Mulyono, P., Prasetya, A., Petrus, H.T.B.M., 2020. Sulfuric Acid Leaching of Heavy Rare Earth Elements (HREEs) from Indonesian Zircon Tailing. International Journal of Technology. Volume 11(4), pp. 804-816

Iga Trisnawati 1. Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika No.2, Yogyakarta 55281, Indonesia 2. Center for Acce
Gyan Prameswara Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika No.2, Yogyakarta 55281, Indonesia
Panut Mulyono Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika No.2, Yogyakarta 55281, Indonesia
Agus Prasetya 1. Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika No.2, Yogyakarta 55281, Indonesia 2. Unconventional
Himawan Tri Bayu Murti Petrus 1. Sustainable Mineral Processing Research Group, Department of Chemical Engineering, Faculty of Engineering, Universitas Gadjah Mada, Jl. Grafika No.2, Yogyakarta 55281, Indonesia 2. Unconventional
Email to Corresponding Author


Solid pollution has been an issue in mineral processing for decade. One of these pollutants is zircon sand mining waste (zircon tailing). Due to the concentration of rare earth minerals in zircon tailing and the increasing demand of REE in advanced technologies, studying zircon tailing as a potential source of REE had become an interest for us. Our experiments consisted of mineral characterization and an alkaline fusion process, followed by a leaching process. The characterization process was carried out to obtain actual information from zircon tailing samples. This process showed total rare earth elements (REEs) content of 58.62%, at 9%, 1%, 1.2%, 1.7%, and 1.5% for Y, Gd, Er, Dy, and Yb, respectively. A sieving process was carried out since it was known that most heavy rare earth elements (HREEs) content occurs at a larger size. The alkaline fusion process was applied with an intent to break the phosphate bonds present in the REE-carrying minerals (xenotime and monazite) and convert phosphate bonds to hydroxide bonds in rare earth metals. During the alkaline fusion process, as much as 75%, 66.45%, and 60% of the phosphate, silica, and zirconium, respectively, were reduced. The leaching process was carried out in a flat-bottom three-neck flask. The optimum point of leaching experiments occurs at 0.5 M H2SO4, 60°C, and a solid-to-liquid (S/L) ratio of 10 g/100 mL. In these conditions, as much as 89%, 99%, 94%, 92%, and 90% of Y, Gd, Er, Dy, and Yb, respectively, were recovered as an HREEs2-(SO4)3 product solution.


Acid leaching; Alkaline fusion; Rare earth elements; Zircon tailing


    The issue of decreasing environmental quality has been an increasing concern recently (Hudson-Edwards and Dold, 2015; Kusrini et al., 2018a, 2018b; Reichl et al., 2018). All fields are affected by this problem—the mining sector included, which leaves waste as a result of mining activities (Durucan et al., 2006; Aznar-Sánchez et al., 2018). This waste has not been treated to reduce environmental pollution, such as tailings from the zircon mining in Indonesia. This tailing waste contains several important elements that are useful for advanced technology and can potentially be extracted from mining waste treatment. Some of these elements are “heavy rare earth elements” (HREEs) (Harjanto  et al., 2013, Hamzah et al., 2018).

   Rare earth elements (REEs) are all elements in lanthanides, totaling 17 elements, including scandium and yttrium. The REEs are divided into two groups, based on atomic weight: the light rare earth elements, which are lanthanum through europium (atomic numbers 57–63), and the heavy rare earth elements, which are gadolinium through lutetium (atomic numbers 64–71). Yttrium (atomic number 39), though light, is included among the heavy REEs group due to its common chemical and physical affiliations with the heavy REEs in nature (Qi, 2018). These elements have chemical and physical properties in common, and they are useful for many advanced technologies, such as superconductors, magnets, and catalysts (Habashi, 1992; Gupta and Krishnamurthy, 2005; Kusrini et al., 2018a; Machmudah et al., 2019). Usually, the separation process cannot be carried out directly to obtain oxides or pure elements from rare earth minerals due to their similarity (El Hady et al., 2016; Kusrini et al., 2018b).

   The existence of rare earth metals (REMs) is not as rare as their name suggests. The presence of cerium (Ce), praseodymium (Pr), samarium (Sm), and Yttrium (Y) is even more extensive than precious metals (gold [Au], silver [Ag], and platinum [Pt]) in the earth’s crust (Lide, 2004). Even at the end of 2018, rare earth oxide production reached more than 150,000 metric tons, but its occurrence in mineable deposits is limited (King, 2013; Haxel et al., 2014; Gambogi, 2019). Therefore, to meet the increasing global demand for REMs, efficient extraction technology from secondary sources is needed.

There are several ways to extract rare earth metals from their carrier minerals, such as direct leaching using sulfuric acid at temperatures of 155–230°C, alkali cracking using a sodium hydroxide solution at 140°C, roasting using sodium carbonate at 900°C, and alkaline fusion using flakes of sodium hydroxide at 400–500°C. The disadvantages of the above extraction processes are: (1) for the direct leaching process using sulfuric acid, the formation of REE  double sulfate cannot be avoided, so it will affect the refining process of REEs, and during this process, the phosphate that binds to the monazite cannot be separated immediately; (2) consumption of sodium hydroxide is too high in the cracking process using sodium hydroxide (REE / NaOH = 1/21); and (3) high energy requirements are prohibitive in the roasting process using sodium carbonate (Sadri et al., 2017). Another process for extracting rare earth elements is the alkaline fusion process. This process is carried out by reacting rare earth minerals with alkali in order to get REE-(OH)3, while the phosphate turns into a Na3PO4 byproduct. The two products can be separated by washing them with water. REE-(OH)3 remains in the solid phase while Na3PO4 dissolves. The alkaline fusion process was chosen for our experiments because it offers several advantages. The main advantage is that the alkaline fusion process can break the phosphate bonds in xenotime and monazite and break the silica matrix to make the leaching process more effective (Biswas et al., 2010; Dai et al., 2014; Tang et al., 2019). Furthermore, rare earth hydroxide (REE-[OH]3) products easily occur through this process. Another advantage is that Na3PO4 can be purified as a byproduct. These conditions are needed to enhance the effectiveness of leaching. The leaching process is performed to dissolve the rare earth element, which ensues at a pH below 3.5 (Amer et al., 2013; Kumari et al., 2015).

        In this experiment, HREEs were extracted from Indonesian zircon tailings. The purpose of this research was to determine the optimum conditions for the leaching of HREEs from alkaline fusion products (HREEs-[OH]3). Pretreatment was carried out through an alkaline fusion process to break the phosphate bonds in HREE (monazite and xenotime) carrier minerals. Then, the leaching process was carried out using sulfuric acid under various leaching conditions.


The process of leaching HREEs was investigated through several parameters, and the optimum conditions were identified. Sample characterization was carried out through the process of sieving and analyzing the composition of the sample using XRF. The pretreatment process was carried out to increase the recovery of HREEs. The pretreatment process includes alkaline fusion and leaching using deionized water. The alkaline fusion process of tailing zircon was completed in three hours at a temperature of 450°C and tailings at an NaOH ratio of 1:1 (wt/wt). In addition, recovery phosphate increased following the pretreatment processes of alkaline fusion, characterized by a 73.57% reduction in phosphate binding to HREEs, followed by the leaching process performed to dissolve HREEs-(OH)3 into a solution of HREEs2-(SO4)3. The optimum leaching conditions in this experiment occurred at concentrations of 2 M H2SO4, 60°C, an S/L ratio of 10 g/100 mL, and 150 rpm during 60 minutes. Under these conditions, HREEs were recovered at as much as 89%, 99%, 94%, 92%, and 90% for Y, Gd, Er, Dy, and Yb, respectively. This experiment is expected to serve as a treatment solution for tailings from zircon sand mining activities and as an alternative solution for processing HREEs from secondary sources.



    The authors are grateful to Universitas Gadjah Mada for supporting this research and also to PSTA–BATAN, Indonesia, for the analytical instruments used to complete this study. In addition, one of the authors, Iga Trisnawati, appreciates financial support from Beasiswa Saintek Kemenristek/BRIN.


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