Developing Vietnam’s mineral sands for the rare earths market

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Published: Monday, 22 September 2014

Vietnam has 3,260km of coastline, along which the main sand deposits containing ilmenite, rutile, zircon and other heavy minerals are distributed. Tran Kim Phuong* outlines how these deposits can be of use for the rare earths — or the TiO2 — market.

Vietnam’s coastal placers, of which 40 have been discovered, are located along most of the country’s coast from Mong Cai (Quang Ninh province) to Vung Tau (Ba Ria-Vung Tau province), hosted by Quaternary sediments.

The main deposits are concentrated along the coast of central Vietnam between Cua Hoi in Ha Tinh province and Ham Tan, in Binh Thuan province. Four deposit groups of economic value have been identified, which include; Ky Anh, Ha Tinh province; Thuan An, Thua Thien-Hue province; Cat Khanh, Binh Dinh province; and Ham Tan, Binh Thuan province.

The average content of ilmenite in the mineral sands is about 30-80kg/square metre, however some locations can contain content up to 200-300kg/square metre or higher. In most placer deposits, fine grain fractions (0.05-0.5mm) are dominant, making up around 80% of the material, with a fairly high quality of ilmenite ores found in Vietnam’s coastal placers.

Spectral analysis of single ilmenite samples is in the region of: tin (Sn) 0.001-0.03%; lead (Pb) 0.01-0.02%; vanadium (V) 0.05-0.1%; zinc (Zn) 0.01%; aluminum (Al) 0.02-0.03%; copper (Cu) 0.001%.; and titanium dioxide (TiO2) content is around 52.6%, which is equivalent to ilmenite ore quality of many countries in the world and similar in content to deposits located in the Manavalakurichi area, India (see Table 1).

Total titanium mineral reserves that have been discovered and explored in Vietnam are estimated at around 26.5m tonnes ilmenite, of which 18m tonnes are in primary ores or in territorial placer deposits and 8.5m tonnes are in coastal placer deposits.



In addition to ilmenite, Vietnam is host to deposits estimated at 600,000 tonnes zircon and 300,000 tonnes monazite, equivalent to 200,000 tonnes rare earth oxides (REO).

More recently, the discovery of titanium and zircon-bearing red sand led to an additional resource estimate of 599m tonnes titanium and zircon in the red and great sand stages along the seashore between Tuy Phong and North Phan Thiet City, Binh Thuan province, South Central Vietnam (Figure 1).

What is notable is that the content of zircon is relatively high, accounting for 11-23% of total heavy minerals (THM), with an average of 19% over the entire investigated area.

Rare earth phosphates (monazite and xenotime) have been noted as a valuable byproduct of ilmenite and zircon mineral sands in coastal Vietnam, particularly in the Thuan An and Cat Khanh areas. The placer deposits with large reserve of monazite are De Gi-Cat Khanh, My Tho, Ke Sung and Quang Ngan. In addition, the deposits of Xuan Thinh-Tuy Phong in Phu Yen province and Cua Dai in Quang Nam province contain reserves of between 1,000 and 4,000 tonnes as well as some occurrences of large content of monazite in Con Dan (15.3kg/square metre) and Nhan Ly (10.9kg/square metre).

Monazite (Ce,La,Y,Th)PO4 is a mineral containing rare earth phosphates of cerium and yttrium, with variable amounts of thorium, and a ratio of cerium oxides of 39-74%, yttrium oxides 0-5% and thoria 0-30%. The mineral ranges from pale yellow to a rich golden brown or black in colour and has a specific gravity ranging between 4.9 and 5.3 and hardness of about five Mohs. Used in many industrial sectors as a source of rare earths, monazite dominates over xenotime in most coastal placers, and has been discovered in four deposit groups of economic value in Ky Anh, Thuan An, Cat Khanh and Ham Tan.

Xenotime (YPO4) concentrates produced are in grade around 92% grade and contain around 35.8% Y2O3. Xenotime is found in Norway in pegmatite veins as well as in Denmark, Sweden, Brazil, Czech Republic, Slovakia, Austria, Germany, Canada, France and Vietnam (see Figure 2).



Quang Ngan

The Quang Ngan deposit is located to the north side of the Thuan An group (Thua Thien in Hue province) and measures 22.5km in length and 513 metres in width with an average thickness of 4.03 metres.

Content (kg/square metre): Ilmenite 19.0-76.2 (averaging 36.93); leucoxene 0.61-8.19 (averaging 3.45); rutile 0.29 -22.9 (averaging 3.92); zircon 1.96-61.4 (averaging 12.49); and monazite 2.11.

Reserves: Ilmenite 139,000 tonnes (probable) and 1.332m tonnes (possible); zircon 18,430 tonnes (probable) and 241,000 tonnes (possible); monazite and xenotime 8,255 tonnes.

Ke Sung

Ke Sung deposit is located along the coastal of village of the same name, 12km south of the Thuan An mouth (Thuan An group). There are two bodies with a total 5,000 metres in length and an average width 250 metres. The uppermost layer of the beach and dunes containing heavy minerals forms the main body of the deposit with thicknesses reaching 3.16 metres.

Content (kg/square metre): Ti-minerals 35.88; ilmenite 31.66; zircon 7.73; and monazite and xenotime 2.97.

Probable reserves: Total Ti-minerals 214,250 tonnes; ilmenite 185,604; zircon 52,307 tonnes; monazite and xenotime 18,343 tonnes.

Vinh My

Vinh My deposit extends 12.5km along the coast from Vinh My village to the Tu Hien mouth (Thuan An group), with the biggest section of width measuring 600 metres and the narrowest 80 metres, with an average width of 210 metres. The uppermost layer of beach sand constitutes the dunes bearing heavy sand with an average thickness of 1.66 metres. The body area is 1,906m square metres.

Content (kg/square metre): Ilmenite 53.3-192.9 (averaging 76.0); zircon 10.0-30.0 (averaging 14.67); monazite and xenotime 1.02.

Chemical composition (%): TiO2 1.07, ZrO2 0.35, SiO2 95.22, SFeO 0.75, MnO 0.06, Al2O3 1.48, Cr2O3 0.05.

Probable reserves: Total Ti-minerals 190,464 tonnes; ilmenite 171,130 tonnes; zircon 34,270 tonnes; monazite and xenotime 2,057 tonnes.



Cua Dai

The Cua Dai deposit in Hoi An city, Quang Nam province, consists of three bodies. The first, in Lap Binh, is 600 metres long with a width of 10-80 metres and a thickness of 1.5 metres. Average ilmenite content of the deposit is between 6-8kg/square metre. The second body is 200 metres long, 50-60 metres wide and 1.4-1.8 metres thick. Ilmenite content in the second body is from 9-11.8kg/square metre. The third measures 100 metres in length, 15-60 metres in width and 1.5 metres in thickness with an ilmenite content of 28-74kg/square metre, averaging 50 kg.

The total has a reserve of 1.08m tonnes, including 0.92m tonnes ore placer and 0.16m tonnes primary and residual weathering ore. Monazite content in the ore placer is 1.334kg/square metre with a reserve of 4.754m tonnes.

My Tho

My Tho deposit is situated along the coast area of the My Thanh, My Tho and My An villages, north of Cat Khanh (Cat Khanh group). Once again there are three ore bodies, A, B and C, coinciding principally with sand dunes, of which body C is the biggest. The body is distributed across an area of 5,523 square metres, with average thickness of 2.68 metres.

Content (kg/square metre): Total Ti-minerals 39.21-49.97 (averaging 46.37); ilmenite 37.61-48.60 (averaging 44.856); zircon 0.95-1.69 (averaging 1.21); monazite and xinotime 1.41.

Probably reserves: Ti-minerals 819,990 tonnes; ilmenite 789,338 tonnes; zircon 22,484 tonnes; monazite and xenotime 50,044 tonnes.

De Gi-Cat Khanh

De Gi-Cat Khanh deposit is situated along the coast of Cat Khanh village (Cat Khanh group), stretching over an area of 8km from De Gi port to Chanh Oai village. The deposit has an average width of 1.2-1.4km. Three ore bodies overlie each other, with an average thickness of 3.5 metres, averaging in Ti-mineral content at 72.91kg/square metre (ilmenite at 70.09kg/square metre), zircon 2.48kg/square metre, monazite and xenotime 5.42kg/square metre.

Probable and possible reserves: Ti-minerals 2.307m tonnes; ilmenite 2.249m tonnes; zircon 78,478 tonnes; monazite and xenotime 193,680 tonnes.



Xuan Thinh-Tuy Phong

The Xuan Thinh-Tuy Phong deposit in Song Cau district, Phu Yen province, belongs to the Cat Khanh group and is two bodies, in which body two is of large economic value. Averaging 2.04 metres in thickness, the second body has a titanium content of 176.50kg/square metre, ilmenite 173.05kg/square metre, zircon 5.72kg/square metre and monazite and xenotime 1.01kg/square metre. The deposit is distributed over an area of 112,000 square metres.

Reserves: 99,108 tonnes, of which monazite and xenotime account for 1,594 tonnes.

Monazite extraction technology

Chemical composition

Xenotime usually exist in two forms, either as a mechanical mixture of monazite or as an independent mineral.

Mozanite consists of high content of Sm, Nd, and Y. Sm can reach quantities of 7.4%, Nd quantities of 17.8% and Y between 1.3 and 4.03%. Microsonic analysis additionally shows that that monazite-xenotime contains heavy group elements in the following quantities: Er2O3 0.2%; Lu2O3 0.1-0.3%; Dy2O3 0.5%; Eu2O3 0.1-0.5%; HO2O3 0.5%; Gd 0-3%; and ThO3 4.8-5.48%.

Processing

In crude beach sand, monazite usually occurs associated with fairly large percentages of ilmenite, and smaller amounts of quartz, rutile, zircon, magnetite, garnet and sillimanite.

For processing, the sands are usually given a preliminary wet concentration and after drying are further separated by a series of powerful electromagnets of varying intensity. Non-magnetic residue, which contains zircon, rutile, garnet and sillimanite, is often treated by other methods for separation.

The Processing Centre of National Atomic Energy Institute of Vietnam has recovered monazite and xenotime, attaining 90-95% content, corresponding to 60-65% total Tr2O3 using a suitable ilmenite and zircon process. Ore quality is not worsted to the marketable products of some countries in the world.

Extraction

Prior to use in manufacture, it is necessary to chemically treat the rare earth minerals for separation and purity.

Monazite is treated by Na(OH) and the hydroxides are separated to make up Ce (OH)4, Nd, Pr (OH)3, La (OH)3, ThO2 and transferring in the pure oxides of Ce, La, Nd and Pr from distinct rare earth products.

Using these in the manufacture of high grade glass has obtained good results in products such as vases and glassware, which require quality guarantees. Properties include a transparent uncoloured glass of refractive index N 1.52, optical penetration of over 99% and yellow coloured, high-lustre glass. Glass made from these elements can adsorb harmful light rays, have colour-changing properties or be used in soldering.

Ce glass is unique as it is not coloured under radioactive light; Pr glass enables the filtering of ultraviolet rays; while Nd glass is used to make safety glass for soldering.

Rare earths from Vietnam are also used in the production of rare earth-ferro alloys, magnesium rare earth intermediary alloys (Figures 2 and 3) rolling pillars, cement crushing balls, and anti-abrasion canvases. In the glass industry, rare earths have been used in the manufacture of optical abrasive powders, magnetic materials or for the enhancement of glass quality.



Prospect of monazite rare earth development in Vietnam

Vietnam’s resources are capable of producing minerals of industrial significance, such as bastnasite, monazite and xenotime. Monazite bears many elements of cerium group (light rare earths), while xenotime has a content of high yttrium group (heavy rare earths).

Vietnam has total reserves of more than 17.2m tonnes REO (consisting of 17m tonnes of primary ore and 200,000 tonnes of coastal placer), in which the resource of category R-1-E is about 980,000 tonnes. In terms of global rare earths resources, Vietnam ranks ninth behind China, Russia, Namibia, the US, Australia, India, Canada and South Africa.

To meet the increasing needs of today’s market, concentrate must have a minimum content of 30% TR2O3 and maximum of 70%. To reach these specifications, Vietnam’s processing sector has worked to perfect technology innovation and investment in new, modern equipment, aiming to supply enough domestic demand as well as enough resources for export.

References:

[1] Do Thi Hoa Lan et al., 1995. Potential of monazite - xenotime rare earth ores in coastal placers of Vietnam, Geology and Mineral resources, Tome 4, p. 231 - 243. Research Institute of Geology and Mineral resources, Ha Noi.

[2] Nguyen Minh Loan, 1988. Titanium deposits, Geology and Mineral resources of Vietnam, p 80 - 103. General Department of Geology, Ha Noi.

* Vietnam Institute of Geosciences and Mineral resources