Diatomite deposits: potential in Vietnam

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Published: Monday, 22 July 2013

Diatomite is found in abundance in several regions of Vietnam; Dr Tran Kim Phuong, of the Vietnam Institute of Geosciences and Mineral Resources explores its industrial importance and the improvements that have been made by filter-aided powder processing.

Diatomite consists predominantly of microscopic siliceous spines of diatomeae algae, although other silica-secreting organisms can sometimes be found. It resembles chalk or clay, but mainly contains silica and between 3-10% water. It is friable, porous and floats on water when dry, while its absorption rate means it can carry between 25-45% water.

Its key properties are its porosity, fineness of pores, absorptive power, leightweight and low-heat conductivity. The mineral is used as a filter and absorber, and has applications in heat and sound insulation, abrasives, building materials, ceramics and chemicals.

Diatomite deposits are present in the southern provinces of Vietnam at Phu Yen (South-Central) and Kon Tum, Lam Dong and Binh Thuan (Highland region), of which the Hoa Loc deposit in Phu Yen is the largest reserve with the highest ore quality.

Preliminary prospecting took place at the Hoa Loc deposit in 1991, with later research work into ore processing and the use of diatomite as a filter aid for discarded oil (lubricant) treatment producing important results.

Total reserves of diatomite in Vietnam are estimated to reach around 130m tonnes, making it one of the world’s largest diatomite resources.

Total global diatomite production in 2012 was estimated at 2.1m tonnes by the USGS, remaining constant with the 2011 level and up from a slight fall of around 10,000 tonnes, to 1.83m tonnes, in 2010. Consistently, the main producers have been the US and China, producing over half of total output. Denmark and Japan both continue to be significant producers.

Countries with an output below 100,000 tonnes include: the CIS, France, Spain, Argentina, Turkey, Iceland and Italy.

The filtration market continues to rely heavily on diatomite, with the mineral accounting for 65% of the market in 2010. Diatomite is also used in absorbents and fillers and prices range from $275/tonne for filter-grade diatomite to $400/tonne for speciality products.

There is a certain threat to diatomite in the filtration industry from a number of substitutes, including expanded perlite and synthetic fibres, but diatomite’s unique properties help it to retain much of the market.





Distribution and potential of Vietnamese diatomite

Connected with young volcanic formations, diatomite, as well as bentonite, deposits only occur in south Vietnam, predominately in the South-Central and Highland regions.

Diatomite deposits in Phu Yen province are distributed in four areas: Hoa Loc, Tuy Duong, Trung Luong and Tra Rang, with total combined reserves of 90m tonnes. The diatomite clays have lacustrine sedimentary genesis in the volcanically-active Neogene period. Diatomite products are used in fields such as drilling fluid, filter-aids for quenched water and as an absorbent material as an environmental treatment for cultivating water products.

Diatomite deposits occur in several locations in the Highland region.

In Kon Tum province, diatomite is found in Neogene sediments, mainly of fine-grained sandstone intercalated with siltstone and well preserved plant-bearing argillite. There are three deposits, Vinh Quang, Phuong Quy and Ia Le, of which Vinh Quang is largest.

The Vinh Quang (Kon Tum town) diatomite-bearing deposits have a thickness of between 3-120 metres, consisting of two narrow bands 2-3km long and 0.2-0.7km wide. The upper bed is two metres thick, comparatively clean-bedded and white to white-grey coloured. It is friable, light and smooth. The lower bed is four metres thick, thin-bedded, greenish-grey to yellowish-grey coloured and mixed with quantities of clay. A bed of clay is present between the two bands.

Mineral composition of the ore is predominately of clean silica, formed by diatomeae spines.

The chemical composition is principally silicon dioxide (SiO2 50.7-60.2%), aluminium oxide (Al2O3 14.03-23.52%), and iron oxide (Fe2O3 9.02-10.62%). It also contains smaller concentrations of elements including calcium oxide (CaO 0.55-0.67%), magnesium oxide (MgO 0.04-0.95%), potassium oxide (K2O 0.85-0.95%), sodium oxide (Na2O 0.1-0.57%), and sulphur trioxide (SO3 0.44-0.87%) and titanium dioxide (TiO2 0.65-0.76%).

The potential resource of Vinh Quang is estimated at 26.19m tonnes.

In Lam Dong province, diatomite is found in the Bao Loc and Di Linh districts. The Dai Lao diatomite deposit in Bao Loc is a large deposit of 12.92m tonnes reserve.

The chemical composition is principally SiO2 (38.34-67.42%), Al2O3 (15.79-28.19%) and Fe2O3 (2.39-15.31%). It also contains smaller concentrations of elements including CaO (0.0-0.67%), MgO (0.01-1.22 %) and TiO2 (0.77-1.24%).

The mineral composition is made up mainly of diatomite (86%), but also contains sericite (20%) and quartz (10%). The deposits have plasticity of 25.75-58.35% and lime attraction of 62.1-98.4mg CaO/100mg soil.

In Lam Son (Bao Loc), there is also a prospective occurrence, with a diatomite bed 2-11.6 metres in thickness, with ore of lime attraction 58.10-100.80mg CaO/100mg soil.

The Da Le diatomite deposit (Di Linh district) occurs in Neogene lacustrine sediments, covered by basalt eruptive rocks of the Pliocene-Pleistocene age. Above and below the diatomite, there are intercalated layers of shale and bentonite clay. The diatomite-bearing stage is 0.2-1.5km wide, around 6km long and stretches from the Da Le bridge to Lang Hanh.

The diatomite clay is yellowish-white coloured, light-porous, easily broken and bears silica algae spines in its composition.

The chemical composition is principally SiO2 (58-62.56%), Al2O3 (13.19-20.12%) and Fe2O3 (2.95-6%). It also contains smaller concentrations of elements including CaO (0.2%), MgO (0.31%), MnO (0.01%), SO3 (0.18%), P2O5 (0.06%), K2O (1.25%) and TiO2 (0.65-0.82%).

The deposit also has a lime attraction of 218.7-753.3mg CaO/g soil at 700oC.

In Binh Thuan province, the Da Kai diatomite occurrence at the Sung Nhon commune, Duc Linh district, is covered by a siltstone layer of grey, ash-grey, greenish colour, confused by a small amount of brown coal from the Neogene era.

The thickness of diatomite layer is between 7-10 metres, while the covering layer is of 12-18 metres thickness. Diatomeae algae remains are very high, up to 90%, with clay minerals at 5-6% and quartz at 3-4%.

The chemical composition is principally SiO2 (56.16%), Al2O3 (19.86%) and Fe2O3 (3.84%). It also contains smaller concentrations of elements including CaO (1.08%), MgO (0.05%), SO3 (0.2%) and TiO2 (1.09%).

The deposit has not yet been evaluated on the reserve scale.

On the whole, the diatomite in South-Central and Highland regions is of a fair quality, and can be used in applications including heat insulations, light aggregate, hydraulic cement, in filters, absorbents, additives in rubber, soap and insecticides and a variety of other applications.

It can also be used in polishing technology, and is particularly applicable against acidic and alkaline corrosion.

As well as this, when heated to 650-750oC, Highland diatomite-bearing sediment is a potential source of pozzolan for use in the cement industry.





Hoa Loc diatomite

The Hoa Loc diatomite deposit located in An Xuan commune, Tuy An district, Phu Yen province in South-Central Vietnam, consists of three ore bodies of industrial value. Each body is 5.5km long, with thickness ranging from 4.3-33.4 metres.

The average density of the crude ores is 1,078 kg/m3, wind dry 0.906g/cm3 and drying at 105oC as 0.730g/cm3.

If calculated after volume mass of wind dry (0.906 g/cm3), the reserve of Hoa Loc diatomite deposit is 61,385,377 multiplied by 0.906 kg/m3, giving 55,616, 975 tonnes.

The SiO2 content in the first body is 64.16%, with Fe2O3 at 4.39%. The SiO2 reduces gradually to the southwest of the body, while the Fe2O3 increases.

In the second body, the average SiO2 content is 62.67%, with an Fe2O3 content of 4.72%. SiO2 content is stable along the direction line.

In the third body, the average content SiO2 is 64.87% and is generally stable along the direction line and follows a deep trend. The Fe2O3 content is 4.89%.

Figures provided by Phu Yen Service of Industry show that the crude ore taken at the diatomite resource is composed of principally SiO2 (67.96%), Al2O3 (12.12%) and Fe2O3 (2.97%). It also contains smaller concentrations of elements including CaO (0.17%), MgO (0.39%), SO3 (0.15%), K2O (0.21%), Na2O (0.17%) and TiO2 (1.17%), according to research by Tran Van Lung 1997.

Hoa Loc provides the highest-quality diatomite when compared with other resources as shown in Table 2.



Technological research of filter-aid powder processing

The Scientific Institute of Materials has carried out research into filter-aid powder processing of the Hoa Loc diatomite through a combination of mechanic floatation and chemical treatment. This consists of two steps:

Step 1: Crude ores are struck to 10mm grain size, ground and rubbed, passed through a 0.25mm sieve to a hydraulic cyclone where

the diatomite is separated from grits and clays (Fig 1).

SiO2 content of concentrate after the separating processing reached 75.74%, an increase of 6.44% compared with crude ore (67.3%), but still with a high iron content of 3.47%.

Step 2: The diatomite concentration is blended with an H2SO4 / HCl (1/1) solution. The acid spend here is 8% wt, the ratio of solid and liquid is 2.5 and the reaction maintaining temperature is 150oC. The reaction maintaining time is 150 minutes, followed by washing for careful sorting and heating at 900oC (Fig 2).

The combination of mechanic floatation and chemical treatment has produced diatomite with SiO2 content of 90.02%, Al2O3 1.6% and Fe2O3 0.35%, equivalent to imported filter-aids from Japan (Radiolite 500 and Radiolite 800) and the US (Hyflo RV) for use in the foodstuff industry.

These results have been used as the basis of a pre-feasibility report named: Plant construction of filter-aids powder production from diatomite ores at the An Phu zone, Phu Yen province.

Testing of discarded lubricant treatment by diatomite powder

The cleaning process of used lubricants reduces or rejects impurities such as dregs, resin, sulphur compounds, aromatic compounds, acids and other matters. The regeneration of used lubricants has, therefore, clear financial benefits, while helping to preserve the environment.

The Phu Yen diatomite powder has been used with four samples of grain sizes:

Sample A1 of grain size > 100 microns (µ)

Sample A2 of grain size from 88 - 100µ

Sample A3 of grain size from 71 - 88µ

Sample A4 of grain size < 71µ

The process involves mixing 500g diatomite powder with 500g discarded lubricant; stirring with speed of 1,500 rounds/minute for 30 minutes at 75-80oC; cooling and settling for between 20-24 hours; decanting the deposit; and concentrifuging the oil portion and rejecting the hovering grains.

Measurement results of the chemico-physical specifications of samples before and after treatment are shown in Table 3.

After treatment of discarded lubricant by diatomite powder with four different grain sizes, the dynamic viscosity of oil samples has reduced from 2.3 to 2.4 centistrokes (cSt).

The index of all alkaline reduces significantly, first with A2 and A3 samples of grain size 88 - 100µ and 71 - 88µ respectively, reducing to 50% compared with the index of all alkaline in the discarded lubricant sample. An explanation of this is that large-mass resin or asphane molecules are attacked and adsorbed by diatomite.

Diatomite samples of different grain sizes all adsorb water strongly, so after treatment of the discarded oil, water content is equal to zero.

Content of undissolved dregs reduces significantly from 66.7% to 83.4%, in which the samples of grain size 88-100µ and 71-88µ are the most effective, reducing from 83.4% to 80.6%.



Conclusions and proposals

The potential of the diatomite in Vietnam is considerable. Of the deposits found in the South-Central and Highland regions, Hoa Loc in Phu Yen province is the largest and yields the highest-quality ore. This means it may be the most suitable for investment and exploitation on an industrial scale.

The success of studies into processing technology of filter-aid powder from Hoa Loc diatomite by combining mechanic floatation and chemical treatment has opened the prospect of this raw material source being of significant use in various industrial sectors, while also being important contributor to environmental treatments.

Foreign investment should be encouraged to aid the effective exploitation and processing of these abundant natural resources in Vietnam.

References

Kieu Quy Nam, 1996. Characteristics of Highland diatomite. In Geology and Natural resource, volume I, p. 265-269. National Center of Science and Technology, Ha Noi.

Nguyen Cuong, 1991. Evaluate - investigating report of Hoa Loc (Phu Yen) diatomite deposit. Vietnam Department of Geology and Minerals, Ha Noi.

Nguyen Duc Quy et al. 2008: Sustainable development of diatomite mineral industry of Vietnam. The 19th National Conference on mining Science and Technology, Proceedings, p. 295-301. Vietnam Mining Science and Technology Association, Ha Noi.

Nguyen Thi Thanh Huyen, Nguyen Van Hanh, Tran Van Lung, 2006. Technological study of filter-aid preparation from the Hoa Loc, Phu Yen diatomite ore. Journal of mining Industry, No 2 - 2006, p. 12-15.

Tran Van Lung, 1997. Study to processing of Phu Yen diatomite ores. Selected scientific works, Tome 24. University of Mining - Geology, Ha Noi.