UTILIZATION OF SLAB QUARRY REJECT LIMESTONE IN CEMENT MANUFACTURE
- A CASE STUDY
D K Panda, N K Sharma, A K Dubey, Richa Mazumdar, A K Mishra
National Council for Cement and Building Materials, India
Abstract
Quarrying operations for raising slabs from flaggy limestone from the limestone
deposits left dumps of huge quantities comprising of limestone, small to big boulders of
different colours thus of different quality, even cement grade limestone along with very less
quantity of kunkur/ clay and other waste material within the area. Limestone lying in these
waste dumps within the limestone deposit area can be utilized for cement manufacture by
adopting suitable mineral processing techniques based on the principles of size reduction and
separation, and the blending technique. This paper depicts the recovery of limestone from
dumps for cement manufacture from a limestone deposit belonging to Kurnool System of Indian
stratigraphy, located in South India where large scale slab quarry operations has already been
carried out. The qualitative and quantitative assessment of the dumps have been carried out
through geological field investigations followed by topographical survey, review of the
exploration borehole analysis, chemical analysis of representative surface and bulk samples
collected from dump site, determination of bulk density of the dumped material and the
recovery factor analysis by adopting dry mineral processing. The average chemical analysis of
surface samples from these dumps shows CaO% and SiO2% ranges from 44.71 to 49.40 and
10.96 to 18.21 respectively and all other major oxides are well within the limits. Mineral
processing studies comprising size reduction and separation (screen) have been carried out for
all the bulk samples using 25mm, 12.5mm, 6.3 mm and 4.75 mm sieves (the choice of sieve
sizes are being based on qualitative assessment) and all the size fractions are analysed
chemically for all the major oxides. The recovery factor for all the bulk samples has been
determined and the average is 84.46%. Based on the field investigations, qualitative analysis of
surface samples and bulk samples from dumps, size analysis, bulk density and recovery factor
analysis, the quantity of the recovered material is estimated. The high silica content limestone
may be used by blending with high grade limestone proportionately by designing of appropriate
raw mix. Thus, a huge quantity of rejects can be utilized for cement manufacture leading to
conservation of mineral and cleaner environment.
1.0
INTRODUCTION
Quarrying operations for raising slabs from flaggy limestone in the limestone deposits
left dumps of huge quantities of slab rejects comprising of limestone of different sizes and
quality, kunkur/ clay and other waste material within the area. Limestone lying in these waste
dumps can be recovered and utilized for cement manufacture by adopting suitable techniques
of mineral processing or blending.
The present paper is based on the study carried out by NCB in an abandoned limestone
slab quarry located in South India.
Geologically the area falls in the Narji stage, Jammalamadugu Series of Kurnool group in
Cuddapah basin. Narji Limestones is the host of all grades of limestone used in the cement and
metallurgical industries. It is mainly divided into three parts i.e. (i) Upper flaggy limestone, (ii)
Middle massive limestone and (iii) Lower flaggy limestone. It is the middle massive limestone
that forms the backbone of the cement industry. Flaggy limestone generally finds its use as
building stone. Occasionally, the flaggy limestone has lensoid bodies that are massive and are of
cement grade. The litho units of the area : soil, pink / purple shale, green limestone, pink
limestone, grey limestone and quartzite. Detailed exploration comprising topographic surveying
(grid pattern, 1:2000), geological mapping (1:2000), surface sampling, drilling of boreholes and
sub-surface sampling were carried out covering the entire area including the slab quarry reject
dumps.
1.1
Slab Quarry Reject Dumps
After extracting the flaggy limestone as well as some portion of massive cement grade
limestone for slab, huge dumps of different quality and size limestone along with the top soil
and kunkur were dumped in scattered manner in and around the area. The image given below
shows the dumped area and the Photographs-1, 2 and 3 show the dumps around the area.
Dumps
Slab Quarry Reject Dumps around the Area.
(this image is taken from a website)
View of Dumps
1.2
Site Investigation
To assess the dumps qualitatively and quantitatively for recovery of limestone from
these dumps to be utilized for cement manufacture, site investigation has been carried out by
taking traverse all along the area where the dumps are lying. Prior to traverse taken, the survey
map, geological map, exploration details including the borehole litho-chemical logs, geological
and mining reports of the area have been reviewed.
1.3
Surface & Bulk Samples
Representative surface samples (11 nos.) and bulk samples (4nos.) have been collected
from the dumps to understand the quality of the dumped materials. Representative samples
have been prepared at site based on the observations of the dumps and their field positions.
The bulk samples have been collected for the study of recovery of limestone and qualitative
assessment of the same which can be utilized for cement manufacture. Bulk density of the
dumped (loose) materials has also been determined at site. The bulk densities of the samples
are 1.54 t/m3 (S-1), 1.68 t/m3, 1.63 t/m3 (S-3) and 1.83t/m3 (S-4) respectively.
2.0
EXPERIMENTS & ANALYSIS
2.1
Surface Samples
The chemical analysis of the representative surface samples (11 nos.) in percentage are
given in Table- 1.
Table-1: Chemical Analyses of Representative Surface Samples collected from Dumps
Samples from
Chemical Analysis (%)
Al2O3
CaO
Dumps
LOI
SiO2
Fe2O3
MgO
Na2O
K2 O
1
36.06
15.83
0.19
0.66
2
35.30
18.21
0.21
0.70
46.30
0.35
0.08
0.12
44.71
0.32
0.07
3
37.46
12.55
0.17
0.14
0.56
48.35
0.31
0.06
0.11
4
35.33
17.36
5
37.00
13.24
0.21
0.50
45.68
0.32
0.07
0.12
0.38
0.50
47.92
0.32
0.07
0.11
6
36.95
7
36.38
13.70
0.21
0.64
47.60
0.32
0.09
0.13
14.86
0.20
0.67
46.90
0.31
0.07
0.15
8
34.74
16.54
0.09
0.51
46.51
0.30
0.07
0.12
9
37.55
10.96
0.20
0.64
49.40
0.34
0.08
0.14
10
36.47
13.04
1.25
2.37
45.96
0.25
0.08
0.18
11
35.99
15.96
0.09
0.57
46.42
0.31
0.10
0.13
Average
36.29
14.75
0.29
0.76
46.89
0.31
0.08
0.13
It is observed from the chemical analysis of the surface samples that all the major oxides
except SiO2 fall well within the specification for cement manufacture.
2.2
Bulk Samples
The collected representative bulk samples are analysed for feed quality followed by
mineral processing of size reduction and separation, and their qualitative assessment in
laboratory scale. The detail experiments are given below:
2.2.1
Sample-1
The bulk sample S-1 comprising of limestone boulders of different size with out any
mixing of kunkur. Thus the sample has been crushed by jaw crusher to get an output size of
25mm. A representative sample has been prepared by coning and quartering method to
determine the feed quality of the sample. The crushed materials have been separated to 3 size
fractions by using 25mm and 12.5 mm sieves. The weight and weight percent of the oversize
and undersize fractions is given in Table-2. The feed quality and chemical analysis of all the size
fractions are given in Table-3.
Table-2: Weight & Weight Percentage of Over Size and Under Size at different Sieve Size
S. No
1.
2.
Size (mm)
25
12.5
Total weight
Weight (kg)
Oversize
Undersize
29.00
203.00
141.00
62.00
232.00
Weight Percentage (%)
Oversize
Undersize
12.50
87.50
60.78
26.72
Table-3 : Chemical Analysis of Different Size Fractions of Sample S-1.
Sample
Size (mm)
LOI
SiO2
S-1 (Feed Quality)
33.64
17.98
S1 – A
+25
34.00
19.65
S1 – B
-25+12.5
35.33
17.31
S1 – C
-12.5
34.86
17.74
The weighted average of SiO2% in recovered material is 17.72%.
Chemical Analyses (%)
Fe2O3
Al2O3
0.62
0.90
0.65
0.42
0.61
0.25
0.71
0.37
CaO
44.82
44.25
45.49
45.25
MgO
0.37
0.38
0.38
0.40
2.2.2. Sample-2
The bulk sample S-2 comprising of limestone boulders of different sizes with small quantity of
kunkur. Separating the kunkur through screening (4.75mm) the rest of the material comprising
the limestone boulders are subjected to crushing in a laboratory jaw crusher to get an out put
size of 25 mm and then separated to 4 size fractions by using 25mm, 12.5mm and 4.75 mm
sieves. The size analysis is given in Table-4 and the chemical analysis are given in Table-5.
Table-4: Weight & Weight Percentage of Over size and Under size at different Sieve Sizes
S. No
1.
1.
2.
3.
Size (mm)
25
12.5
4.75
Total weight
Weight (kg)
Oversize
Undersize
41.00
230.00
153.00
77.00
61.00
16.00
271.00
Weight Percentage (%)
Oversize
Undersize
15.13
84.87
56.46
28.41
22.51
5.90
Table-5: Chemical analysis of different Size Fractions of Sample S-2
Sample
Kunkur
Feed Quality
1–A
1–B
1–C
1–D
Size (mm)
+25
-25 +12.5
-12.5 +4.75
-4.75
LOI
29.61
31.94
34.99
34.91
33.87
31.32
SiO2
23.62
21.45
17.77
17.55
18.73
22.38
Chemical Analyses (%)
Fe2O3
Al2O3
4.42
3.04
2.93
1.80
0.95
0.49
1.09
0.46
1.92
0.97
3.25
1.95
CaO
36.60
39.88
44.74
44.87
42.98
38.96
MgO
0.70
0.58
0.38
0.38
0.49
0.59
The weighted average of SiO2% in the recovered materials (+4.75mm) is 17.87%.
2.2.3. Sample-3
The bulk sample S-3 comprising of limestone boulders of different sizes with small quantity
of kunkur. Separating the kunkur by screening at 6.3mm, the rest of the material comprising
the limestone boulders are subjected to crushing in a laboratory jaw crusher to get an out put
size of 25 mm and separated to 3 size fractions by using 25mm and 12.5mm sieves. The size
analysis is given in Table-6 and the chemical analysis are given in Table-7.
Table-6: Weight & Weight Percentage of Over size and Under size at different Sieve Sizes
S. No
Weight (kg)
Oversize
Undersize
30.00
182.00
143.00
39.00
212.00
Size (mm)
1.
1.
25
12.5
Total weight
Weight Percentage (%)
Oversize
Undersize
14.15
85.85
67.45
18.40
Table-7: Chemical Analysis of different Size Fractions of Sample S-3
Sample
Kunkur
Feed Quality
1–A
1–B
1–C
Size (mm)
LOI
31.25
33.93
33.56
34.35
34.12
+25
-25 +12.5
-12.5
SiO2
23.67
19.93
20.10
18.66
18.14
Fe2O3
1.52
0.74
0.62
0.60
0.64
Al2O3
1.66
0.40
0.44
0.33
0.66
CaO
40.23
43.88
44.26
45.03
45.18
MgO
0.47
0.38
0.34
0.36
0.37
The weighted average of SiO2% in recovered material is 18.76%.
2.2.4. Sample-4
The bulk sample S-4 comprising of limestone boulders of different size with soil/
kunkur. Separating the kunkur by screening at 4.75 mm, the rest of the material comprising the
limestone boulders are subjected to crushing in a laboratory jaw crusher to get an out put size
of 25 mm and seprated to 4 size fractions by using 25mm, 12.5mm and 4.75 mm sieves. The size
analysis is given in Table-8 and the chemical analysis are given in Table-9.
Table-8: Weight & Weight Percentage of Over size and Under size at different Sieve Size
S. No
Weight (kg)
Oversize
Undersize
34.00
236.00
158.00
78.00
53.00
25.00
270.00
Size (mm)
1.
2.
3.
25
12.5
4.75
Total weight
Weight Percentage (%)
Oversize
Undersize
12.59
87.41
58.52
28.89
19.62
9.27
Table-9: Chemical Analysis of different Size Fractions of Sample S-4
Sample
Kunkur
Feed Quality
1–A
1–B
1–C
1–D
Size (mm)
+25
-25 +12.5
-12.5 +4.75
-4.75
LOI
27.51
32.49
33.52
35.25
33.21
28.90
SiO2
32.02
22.80
20.99
17.28
21.17
29.66
Fe2O3
2.16
1.01
0.74
0.51
1.05
1.81
Al2O3
4.09
1.90
1.06
0.96
1.61
3.57
CaO
32.21
40.41
42.50
44.92
41.64
34.16
MgO
0.50
0.43
0.41
0.38
0.43
0.51
The weighted average of SiO2% of recovered material (+4.75) is 18.63%.
3.0
RESULTS AND OBSERVATIONS
3.1
Recovery Factor Analysis
Sample- S-1: It is observed that the limestone boulders of different sizes from these dumps
can be raised directly with out any beneficiation process of screening, thus considering 100%
recovered limestone. It is observed that except SiO2 all other major oxides satisfy the
specification. This can be blended with low silica limestone (high grade sweetener)
proportionately to obtain the desired quality.
Sample- S-2: It is observed that the reject from this sample is 53 kg or 17.21%. The size
fraction of -4.75 shows very high silica and low CaO content hence only 82.79% can be
recovered for utilization in cement making subject to blending with sweetener proportionately.
Sample- S-3: It is observed that the reject from this sample is 67 kg or 26.91%. All the size
fractions show silica more than 18%. The limestone can be blended with high grade (sweetener)
limestone proportionately to achieve the desired quality.
Sample- S-4 : It is observed that the reject from this sample is 54 kg or 18.06% . It is observed
that the size fraction of -4.75 shows very high SiO2 i.e. up to 29.66% and low CaO content. The
size fraction +25mm and -12.5mm also show very high SiO2 content. Some percentage of this
limestone may be utilized if blended with high grade limestone proportionately. For utilizing this
limestone sufficient high grade limestone to be blended and Raw mix design to be prepared/
maintained for achieving good clinker.
It is observed that the average reject of the dumped material is 15.54%. However all the
samples collected from the site contain high SiO2% that do not meet the specification as
mentioned above and hence these recovered limestone are of marginal grade and may be
utilized after blending with high grade limestone.
3.2
Quantitative Assessment of the Recovered Limestone
Based on the field investigations, qualitative analysis of surface samples and bulk
samples, size analysis, bulk density and recovery factor analysis, the quantity of the recovered
material is estimated by geological section (10 m interval) method and considering average bulk
density as 1.67. The total quantity (approximate) of the materials in all the dumps of the study
area is estimated at 1.083 million tonnes. It is observed that 15.54% of material is considered as
totally rejects and considering material handling loss of about 5%, the total reject is 20%. The
recovery factor is considered as 80%. The estimated reject is 216646 tonnes and the recoverable
material is 866600 tonnes.
4.0
CONCLUSIONS
It is observed from the detailed systematic and scientific qualitative and quantitative
assessment of the dumps, the dumped materials comprise of limestone of different qualities which
may be utilized up to 80% of the total dumped material for cement manufacture subject to
adopting screening and blending techniques. Similar studies can be carried out for all such dumps
to utilize huge quantities of slab quarry rejects for cement manufacture, thus conserving mineral
resources and cleaner environment.
5.0
ACKNOWLEDGEMENT
The authors have freely drawn upon the completed R&D reports of NCB. This technical paper is
published with the permission of Director General, National Council for Cement and Building
Materials (NCB), India.
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