Journal of Minerals & Materials Characterization & Engineering, Vol. 8, No. 9, pp 701-713, 2009 Printed in the USA. All rights reserved
Evaluation for the Beneficiability of White Silica Sands from the
Overburden of Lignite Mine situated in Rajpardi district of Gujarat, India
M. Sundararajan*, S. Ramaswamy and P. Raghavan
National Institute for Interdisciplinary Science and Technology,
(Council of Scientif ic and Industrial Research), Trivandrum – 695019, India.
*Corresponding Author:,
A representative feed sample of White Silica Sand was wet-sieved in order to recover the desired
fractions for glass making. BIS specification shows that (–600, +300)
m] fraction [A] should
not be more than 50% and (–300, +125)
m fraction [B] should be 50% minimum. The mass
percentage of A and B is found to be 29.9 and 70.1% (ratio =1:3.34) which satisfies the size
specifications for glass making sand. Hence, this ratio was maintained for all the down stream
processing studies. ‘Wet Sieved desired Fraction for White sand’ (WSDFw) was subjected to
attrition followed by magnetic separation. Tests at optimum conditions gave a non-magnetic
fraction (Silica sand product) which analysed 98.1% silica with 0.09% Fe2O3, 0.13% TiO2 and
0.17 LOI. This is found to be matching wi th IS specifications for Grade III sand.
Key words: White silica sand, Beneficiation, XRD, SEM, Magnetic separation
Silica sands, perhaps, has got the most diversified use among all the non-metallic minerals. This
is because of its common occurrence around the world, distinctive physical characteristics such
as hardness, chemical and heat resistance as well as low price. Silica bearing rocks and minerals
such as quartz, quartzite, silica sand together with other varieties of silica like agate, amethyst,
jasper, flint etc. are used in a host of industries such as glass, ceramics, foundries, ferro-alloys,
abrasives, refractories, ornamentation etc. One of the first to use silica sand is in the glass
industry. At least 4000 years ago, long before iron was smelted; glass-making was already a
known craft. The oldest known specimens of glass was obtained from Babylon (2600 B. C.) and
702 M. Sundararajan, S. Ramaswamy and P. Raghavan Vol.8, No.9
from Egypt (2500 B. C.). It could be conclusively proved that the glass-making was well
established in these countries by around 1500 B. C. [1-4].
Silicon, the main constituent of silica does not occur in free state. But silicon compounds are
abundantly available and constitute about 28% of the earth’s crust. The range of silica raw
materials occurring in nature is quite extensive. The silica, SiO2, occurs in different forms such as
quartz, (crystalline); chalcedony, agate, flint and jasper (crptocrystalline), and opal (hydrous
form); sandstone (sedimentary deposit composed of small grains of quartz); quartzite
(metamorphosed derivative of sandstone) and silica sand (weathered sandstone or quartzite
enriched in silica). The silica sand is an assemblage of individual silica grains in the size range
up to 2mm. Sand can be formed in nature by natural weathering of sandstone and quartzite or
mechanically by crushing a sandstone /quartzite or by a process of flotation whereby the various
constituents in a pegmatite or kaolin mixture are separated.
The occurrence of silica sand in world is widespread and extensive. Good quality silica sand
reserves are situated in UK, Germany, Belgium, France, Brazil etc. Silica sand is available
almost in all the states of India. Important deposits are in Andhra Pradesh, Bihar, Goa, Gujarat,
Haryana, Karnataka, Kerala, Madya Pradesh, Rajasthan, Tamil Nadu, Uttar Pradesh, Kerala etc.
Haryana is the leading producer followed by UP and Maharashtra. Silica sand also occurs in
association with clays and quite often as admixture with siliceous or lignitic overburden.
The uses of silica sand depend on its mineralogy, chemistry and physical properties. It is mainly
used for making glass and glass fibre, silicon carbide, sodium silicate, Portland cement, silicon
alloys and metals, filter media in water treatment, sand paper and also for foundry sand,
hydraulic fracturing, sand blasting, paint and a host of other applications.
A major portion of silica sand produced is consumed by glass industry. Important types of
glasses made are sheet, flat, bottle, wired and figured, vacuum, laboratory, fibre, shell, flint,
ophthalmic, beads etc. There are both physical and chemical specifications for each use.
American Ceramic Society and US Bureau of Standards also give detailed chemical
specifications for silica sand for making different types of glasses. After glass, perhaps,
maximum standardization have been made for foundry applications. Silica sand is used in both
foundry cores and moulds because of its resistance to thermal shocks. Physical properties of the
sand is far more important here than the chemical. Silica content of 85% is used in iron castings
while for steel foundries it should be minimum 95%. Silica particle size distribution and grain
shape are very much important for foundry application.
Impurities usually present in the silica sand are free and coated iron oxides, clay, titania and
smaller amounts of sodium, potassium and calcium minerals. The iron, being the most
detrimental impurity, can be reduced by a number of physical, physico-chemical or chemical
Vol.8, No.9 Evaluation for the Beneficiability of White Silica Sands 703
methods, the most appropriate method depends on the mineralogical forms and distribution of
iron in the ore [5-8]. Upgrading of silica sand requires partial removal of iron, and other minerals
which are detrimental to its end use. While much of the liberated impurities can be reduced or
removed by physical operations such as size separation (screening), gravity separation (spiral
concentration), magnetic separation etc., some times, physico-chemical (flotation) or even
chemical methods (leaching etc.) are to be adopted for effective removal of iron which may be in
intimate association with the mineral quite often superficially.
The aim of this investigation is to adopt simple, cost effective as well as environment-friendly
processes and operations for value addition of the sand so that even a small/medium level
entrepreneur can set up a beneficiation plant without much capital investment. For the same, it
was also decided to employ sieving (screening) and other physical operations as far as possible
without going for chemical processing.
The investigation for proving the beneficiability of GMDC White silica sands was initiated by
blending the representative samples which were collected by the supplier of the sample (M/S
Gujarat Mineral Development Corporation, Ahmedabad, India). The sand is the overburden of a
lignite mine situated in the Rajpardi district of Gujarat. Each sample was prepared by thoroughly
blending the material by ‘centre displacement method’ so as to obtain apparently a homogenous
material. 100 kgs of the sand is heaped at one spot and then the entire material is heaped on a
second spot by shovelling (thus displacing the centre). This is repeated for 10 times (five heaps
at each spot). By this, it is assumed that uniformity is achieved.
Standard wet chemical methods supported by instrumental analysis were adopted for
determining the chemical constituents. The samples were analyzed for silica, alumina, loss on
ignition and oxides of iron, titanium, calcium, sodium and potassium. Silica was estimated
gravimetrically by volatilizing with hydrofluoric acid, alumina by complexometric (indirect
EDTA) titration, iron and titanium by spectrophotometry and calcium, sodium and potassium by
flame photometry.
X-ray diffraction (XRD) of the powder sample provides one of the easiest and semi quantitative
methods of identifying the minerals present in clays. The powder XRD patterns were obtained on
a diffractometer (Philips analytical) using Cu Kα radiation operating at 40KV and 20mA on a
diffraction range 5-600 (2θ). Quartz minerals were observed using scanning electron microscope
(SEM) for morphological studies. The grains were mounted on a SEM brass stub. The mounted
quartz grains were coated with gold in a vacuum evaporator while the sample was being slowly
rotated. Usually 15-20 grains were studied in detail and typical micrographs were taken by using
JEOL JSM-5800 scanning electron microscope. The relative densities and relevant bulk densities
of the feed and various intermediates and final products were determined by standard methods.
704 M. Sundararajan, S. Ramaswamy and P. Raghavan Vol.8, No.9
3.1 Characterization
A small amount of sample is drawn from the blended bulk for different characterizations such as
determining their chemical constituents, mineral contents and physical properties. The XRD
pattern of white sand showed the presence of large amount of highly crystalline quartz form of
silica (Fig. 1).
Q-Quartz, K- Kaolinite
Figure 1. XRD pattern of White silica sand
The only other peak visible is that of kaolin (clay). However, it is to be understood that the
height and sharpness of the XRD peak is a measure not only of the quantity of the mineral but
also its higher crystallinity. So the presence of minor phases, quite often, may not be visible in
XRD. SEM studies reveal that the quartz grains are angular to sub rounded marked by peeling of
surface as a result on intense chemical weathering, angular grain with smoothed edges and sides,
weathered, and conchoidal blockage with smoothed surface (Fig. 2 ) were created by mechanical
abrasion and chemical processes.
Vol.8, No.9 Evaluation for the Beneficiability of White Silica Sands 705
(a) Grains are showing angular (b) Peeling of surface as a result on intense
to sub rounded. chemical weathering.
(a) Angular grain with smoothed (d) Semi rounded grain with weathered surface
edges and sides
(e) Conchoidal blockage with smoothed surface.
Figure 2. Scanning Electron Micrographs of white silica
706 M. Sundararajan, S. Ramaswamy and P. Raghavan Vol.8, No.9
Raw white sand was subjected to chemical analysis before starting the beneficiation experiments
(Table 1).
Table1. Chemical analysis of raw white silica sand
Constituents Wt, %
SiO2 91.5
Fe2O3 1.4
TiO2 0.74
Al2O3 4.22
Na2O 0.16
2O 0.01
CaO 0.6
LOI 1.37
Specific gravity of raw sand - 2.83
Silica is relatively low and iron and alumina are on higher side. The presence of small amounts
of sodium, potassium and calcium minerals are also revealed. The loss of ignition (LOI) is
1.37%. The specific gravity was determined as 2.68. Again at each stage of processing, the
products were analyzed for the chemical constituents so that the extent of value addition or
suitability of the beneficiation product with respect to standard specifications could be evaluated.
Properties like particle size distribution and chemical assay of the sand are important for the
glass making. Characterisation showed that this sample cannot directly be used for any value
added ceramic applications.
3.2 Laboratory Beneficiation Studies
Laboratory investigation studies were initiated after the completion of characterisation studies on
the representative raw sand sample. BIS has put forth specifications for four grades of silica sand
for glass making (Table 2).
Vol.8, No.9 Evaluation for the Beneficiability of White Silica Sands 707
Table 2. Indian Standard specifications for glass making sands – 2nd
Revision [IS 488: 1980]
(i) Chemical analysis
(% by mass)
Grade I Grade II Grade III
1 Loss on ignition, Max. 0.5 0.5 0.5 0.5
2 Silica (as SiO2), Min. 99.0 98.5 98.0 97.0
3 Iron Oxide (as Fe2O3), Max. 0.02 0.04 0.06 0.10
4 Aluminium Oxide (as Al2O3),
* * * *
5 Titanium Dioxide ( as TiO2),
0.10 0.10 0.10 *
6 Manganese Oxide (as MnO) To pass the
To pass the
To pass
the test
To pass the
7 Copper Oxide (as CuO) To pass the
To pass the
To pass
the test
To pass the
8 Chromium Trioxide (as Cr2O3) To pass the
To pass the
To pass
the test
To pass the
* These requirements shall be as agreed to between the purchaser and the supplier
(ii) Size grading Wt, %
Retained on 1 mm IS sieve - Nil
Retained on 600 micron IS sieve, % by mass, Max. -01.0
Passing through 600 micron IS sieve,
but retained on 300 micron IS sieve, % by mass, Max. -50.0
Passing through 300 micron IS sieve,
but retained on 125 micron IS sieve, % by mass, Min. -50.0
Passing through 125 micron IS sieve, % by mass, Max. -05.0
The best grade known as Special grade should contain minimum 99% silica with maximum
permissible level of 0.02% Fe2O3 and 0.1% TiO2 for a size fraction in between 600 and 125μm.
Others Grade are low in purity.
3. 2. 1 Wet sieving and mixing of ‘desir ed fractions’ (DF)
Wet sieving was carried out in tune with the requirements for glass making sand and hence the
sieves selected were 1000, 600, 300 and 125μm. The data are given in Table 3.
708 M. Sundararajan, S. Ramaswamy and P. Raghavan Vol.8, No.9
Table 3 Wet sieve analysis of White raw silica sand sample and chemical characterization
of ‘wet-sieved desired fractions’ (WSDFw)
Sieve Size, %Wt.
+1000 0.4
-1000, +600 12.2
-600, +300 24.2
-300, +125 56.7
-125 6.5
%Wt. SiO2 Fe2O3 TiO2 Al2O3 Na2O K2O CaO LOI
WSDFw 80.9 94.2 0.27 0.4 0.4 0.32 0.066 0.61 0.43
The fraction above 600μm, which is about 12.6% of the feed sample, is the coarse grits and is
taken separately since it is not suitable for glass making (This may be used for land filling).
Similarly, the fraction below 125μm (~6.5% of feed sample) which contains mostly kaolin (clay
mineral) is also rejected since the same is also unsuitable for glass making. The weight fraction
of –600 +125μm ‘cut’ is about 80.9%, which, as per the size specification, is the ‘Desired
Fraction for the White silica sand’. We shall denote it as ‘WSDFw’ since it is wet-sieved. As per
BIS specifications, in WSDFw, while -600, +300μm is 29.9%, the other fraction (-300, +125μm)
is 70.1%. This satisfies the IS specifications for the size fractions. Though the mass proportion
as per the specification is satisfied, the chemical analysis (Table 3) showed that the material is
still not suitable for any glass making, hence WSDFw was subjected to further processing.
3. 2. 2 Attrition and magnetic separation
Since the combined iron was found to be mainly as coating on the surface of the sand grains, it
was decided to go for attrition followed by magnetic separation. Attrition tests are carried out in
Netzsch, PE 075, mill which is a vertical cylindrical attritor jar fitted with a specially designed
agitator. The mill was charged with 1.24 Kgs. of the attrition medium, viz., fused ceramic beads
of 1-1.3 mm size and later on, the material was added to the mill in slurry form. The agitator was
switched on and was brought to the required rpm. The mill has got external cooling system for
removing the heat generated during the attrition process. After the completion of the set time, the
total charge was taken out and the attrition media was separated from the slurry by sieving.
For the tests with GMDC White silica sand, the agitator rpm was kept at 1150 so as to generate a
small vortex at the centre of the attritor jar. Two variables were studied: ‘slurry solid loading’
and the ‘attrition time’. Solid loading was varied from 10 to 55%. Towards 55%, externally
Vol.8, No.9 Evaluation for the Beneficiability of White Silica Sands 709
circulated cooling water of the attritor jar was getting heated up and at 60%, the contents did
not move at all due to high viscosity. Hence the optimum solid loading was taken as 50%. Data
is presented in Table 4. Table 5 shows the pattern of the liberation and removal of iron minerals
with respect to attrition time. It could be seen that about 10 minutes was enough to get an iron
value of 0.17%.
Table 4. Influence of solid loading on attrition, impurity libera t ion and removal
Solid loading, Wt% Non-magnetic product
%SiO2 %Fe2O3 %TiO2
15 95.6 0.261 0.381
35 95.9 0.233 0.361
45 96.3 0.204 0.340
50 96.8 0.170 0.320
55 96.9 0.168 0.318 – Cooling water
getting heated up
60 Could not be subjected to attrition due to infinite viscosity
Fixed conditions: Media -1.24 Kg., Size-1-1.3mm fused ceramic beads;
Attrition time –10 minutes, agitator rpm-1150
Magnetic separation: Magnetic field (equivalent current in Amp.) – 3.2
Medium: Iron balls (diameter of 6.3 mm) -1.248 Kg.
(Total slurry volume – 250 ml)
Table 5. Influence of attrition time on impurity liberation and removal
Attrition time, minute’s Non-magnetic product
% SiO2 % Fe2O3 % TiO2
5 95.1 0.268 0.392
10 96.9 0.170 0.320
15 96.9 0.168 0.316
20 97.0 0.168 0.310
30 97.1 0.167 0.309
Fixed conditions: Attrition Media -1.24 Kg., Size-1-1.3mm fused ceramic beads;
% Solids loading –50; agitator rpm-1150
Magnetic separation: Magnetic field (equivalent current in Amp.) – 3.2
Attrition Medium: Iron balls (diameter of 6.3 mm) -1.248 Kg.
(Total slurry volume – 250 ml)
710 M. Sundararajan, S. Ramaswamy and P. Raghavan Vol.8, No.9
The attrition media was removed by sieving the product slurry using a 600μm sieve. No sand
was found along with the recovered media. Again the whole slurry was passed through a 125μm
sieve so as to remove the liberated iron impurities along with some over-ground (fine) sand. The
attrited sand after the removal of attrition medium and -125μm fraction analysed 96.9 % silica,
0.17% iron and 0.32% of titania (Table 6). Though the impurity level has been reduced, the silica
content is still below the required level and the iron value is more than the specified value.
Table 6. Chemical analysis of attrited white sand
Constituent Wt %
SiO2 96.9
Fe2O3 0.17
TiO2 0.32
Al2O3 0.30
Na2O 0.004
2O Below detectable limit
CaO 0.002
LOI 0.2
Due to attrition, a small percentage of sand was overground to below 125 micron. Similarly,
small quantity of attrition medium got broken and damaged. This is evident from the particle
size distribution of the sand before and after attrition which is presented in Table 7.
Table 7. Particle size distribution before and after attrition (White sand)
Sieve Size, %Wt.
Before After
attrition attrition
-600, +300 29.9 28.7
-300, +125 70.1 67.2
-125 Nil 3.5
It could be seen that about 3.5% of –125μm fraction was generated which was removed by
screening through 125 micron screen. The new mass distribution between desired fractions (i.e.,
-600 +300 and –300 +125μm) after the elimination of -125μm is 29.7 and 70.3% respectively.
During attrition, the mass ratio changed only negligibly, so it does not affect the size
As already stated above, attrition operation generates a sand fraction of about 3.5% below
125μm. This is considered to be a loss here, since fraction below this size cannot be used for
Vol.8, No.9 Evaluation for the Beneficiability of White Silica Sands 711
glass making however. If clay is removed effectively, this fraction can be used for some foundry
applications). This is equivalent to 2.8% w.r.t. the original raw sand sample. This includes the
liberated iron and titanium minerals which is, relatively, a very small quantity. The attrition
media loss has been estimated to be about 1.5%.
3.2.3 Magnetic separation
A wet high intensity magnetic separator (WHIMS) which can generate an optimum magnetic
field of 1.8 Tesla (18000 Gauss) at a maximum input current of ~3.2 Ampere was used for
magnetic separation. The magnetic separation, which is integral with the attrition, was carried
out using a Carpco machine which was operated on batch basis. The ‘canister’ (separating
chamber) of the magnet was filled with the medium which, in the present case, is iron balls
(1.248 Kg.) of about 6.3 mm in diameter (small size) and the magnetic field was generated by
switching on the current. The dry sample was spread on the top of the medium and water was
added manually and uniformly on the surface so that it wets the material and takes it through the
voids among the balls. The water equivalent to a 25% slurry was added initially. The liberated
magnetic particles were caught by the balls and the sand slurry flows through the medium down
to the collection pot unaffected by the field. Plain water was added into canister over the balls as
wash water in order to dislodge the sand particles entrapped among the balls. The washings were
collected along with the non-magnetics, i.e., product sand. After the product sand was collected,
the magnetic field was removed by switching off the current and the canister was flushed with
water in order to dislodge the magnetics (iron impurities) from the medium. Later on, the
attrition media (iron balls) were taken out and again washed to collect the final traces of the
sticking iron particles. Both the magnetics (impurities) and non-magnetics (product sand)
materials were dried and weighed. Removal of iron from White silica sand by various processing
methods are given in Table 8. Table 9 shows the stage wise enrichment of silica in the sand by
these operations.
Table 8. Pattern of Iron removal from White sand by Processing
Material Operation %Fe2O3 Cumulative
removal, %
Raw white sand Nil 1.4 Nil
WSDFw Sieving & Mixing
of desired fractions 0.27 80.7
Attrited sand Attrition+Sieving 0.17 87.8
Product White sand
(Non-Magnetics) Magnetic separation 0.09 93.6
712 M. Sundararajan, S. Ramaswamy and P. Raghavan Vol.8, No.9
Table 9. Enrichment of silica in White silica sand due to Processing
Material Operation Silica assay % Cumulative Enrichment %
(Based on 100-91.5 = 8.5 units)
Raw white sand Nil 91.5 Nil
WSDFw Sieving & Mixing
of desired fractions 94.2 31.8
Attrited sand Attrition+Sieving 96.9 63.5
Product White sand
(Non-Magnetics) Magnetic separation 98.1 77.6
WSDFw after attrition followed by magnetic separation at optimised conditions was found to
satisfy Grade III specification for glass making only since the iron content could not be reduced
below 0.09%. Salient results of tests such as LOI, chemical assays and size grading are given in
Table 10 in comparison with BIS specifications. The Product of beneficiation is ‘Grade III glass
making sand’. The coarse grit generated during the sieving (screening) can be considered as by-
Table 10. Comparison of product White sand with the specifications for ‘Grade III’ glass
making sand
(i) Chemical
(% by mass)
Product White
sand (After
IS Specification
for grade III
1 Loss on ignition,
0.17 0.5
2 Silica (as SiO2),
98.1 97
3 Iron Oxide
(as Fe2O3), Max.
0.09 0.1
4 Aluminium Oxide
(as Al2O3), Max.
0.28 ----
5 Titanium Dioxide
( as TiO2), Max.
0.13 ----
6 Manganese Oxide
(as MnO)
---- To pass
the test
7 Copper Oxide (as
---- To pass
the test
8 Chromium Trioxide
(as Cr2O3)
---- To pass
the test
Vol.8, No.9 Evaluation for the Beneficiability of White Silica Sands 713
(ii) Size grading (Table. 10 continued)
Product sand
IS Specifications (After Magnetic separation)
For Grade III Sand
*Retained on 1 mm IS sieve Nil Nil
*Retained on 600 micron IS sieve,
% by mass, Max. 1.0 Nil
*Passing through 600 micron IS sieve,
but retained on 300 micron IS sieve,
% by mass, Max. 50.0 29.7
*Passing through 300 micron IS sieve,
but retained on 125 micron IS sieve,
% by mass, Min. 50.0 70.3
Passing through 125 micron IS sieve,
% by mass, Max. 5 Nil
3.3 Suggested Beneficiation Flow Sheet for White Silica Sand
Based on the laboratory processing studies conducted on the blended raw sand sample for
establishing beneficiability of GMDC White silica sand, an beneficiation flow sheet is suggested
as follows.
The overburden sand is first wet-screened using a single deck vibrating screen having a 600 μm
screen. The oversize grits are collected separately to be used as a land fill while the undersize
slurry is pumped to a second stage double deck vibrating screen fitted with 300 and 125 μm
screens. Both +300 and (-300 +125) fractions are taken together and this slurry after adjusting
the pulp density is sent to attrition mills. The attrited sand slurry is screened using a vibrating
screen fitted with 600 μm screen in order to remove the attrition media. If required additional
water can be added at this stage. The sand slurry is again passed through 125 μm vibrating
screen so as to remove the slimes which contains a major portion of the liberated iron and some
broken attrition media as well as over-milled silica sand particles. The desired fraction (-600
+125μm), after adjusting pulp density is pumped to wet magnetic separators to remove the
remaining iron impurities. The non-magnetic slurry containing the desired silica sand fraction is
collected and pumped to the hydrocyclones for first stage de-watering and finally to a spiral
classifier for 2nd stage and final dewatering to obtain Grade III glass making sand as the principal
714 M. Sundararajan, S. Ramaswamy and P. Raghavan Vol.8, No.9
product. The coarse grits from the 1st screen can form a by-product which can be used for land
The investigation was carried out on White silica sand in order to evaluate their beneficiability
for value addition. Initial characterisation showed that the main impurities in the sample are iron
and titania minerals. The results of beneficiation studies reveal that while wet sieving/screening
removes majority of these contaminating minerals to give an intermediate product sand, attrition
and magnetic separation are required to upgrade the same to grade III glass making sand. Coarse
grits (+600μm) can be considered as a by-product which can be used as landfill. Based on the
laboratory study, beneficiation flow sheets have been suggested for the white silica sand.
The project team is grateful to the sponsors, Gujarat Mineral Development Corporation Science
and Research Centre, Ahmedabad for financial support for the work. They are particularly
thankful to Mr. S.B. Vora who has shown a keen interest in this work. The guidance and advice
received from Shri. CPS Nair, Project Advisor is gratefully acknowledged. Finally, we thank the
Director, NIIST (RRL), Trivandrum for his support for execution of the project.
1. Indian Bureau of Mines, Nagpur, , 1993, Quartz and Silica Sand; Bulletin No. 25
2. Directorate of Mining and Geology, Kerala; 1998. “Report on silica sand”
3. Bureau of Indian Standards, 1977. IS specification for standard silica sand for raw material
testing in foundries, IS:3018-1977, Indian Standard Institution, New Delhi
4. Bureau of Indian Standards, 1980. IS specification for glass making sands, IS:488-1980,
Indian Standard Institution, New Delhi
5. Ay, N., Arica, E, 2000. “Refining Istanbul’s silica sand”, www.Ceramicbulletin. org,
August 06.
6. Farmer, A.D., Collings, A.F., Jameson, G.J., 2000. The application of power ultrasound to
the surface cleaning of silica and heavy mineral sands, Ultrasonics Sonochemistry, 7, pp.
7. Taxiarchaou, M., Panias, D., Douni, I., Paspaliaris, I., Kontopoulos, A., 1997. Removal of
iron from silica sand by leaching with oxalic acid, Hydrometallurgy, 46, pp.215-227
8. Wills, B. A. 1998. Mineral processing Technology. Pergamon Press, New York