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