A Brief Account of Cement Industry in India and the Norms for Suitability of Limestone Deposits for Cement Manufacture

 

S. Vijaya Chitra*

Department of Geology and Mining, Government of Tamil Nadu, Guindy, Chennai.32

*Corresponding Author E-mail: vijchitra@yahoo.com

 

ABSTRACT:

India's long history, dating back to 3200 BC has been influenced considerably by the deposition, development and use of stones and other construction materials.The metallurgical and mineral industries constitute the bedrock of industrial development as they provide the basic raw materials for most of the industries. India produces as many as 84 minerals comprising 4 fuels, 11 metallic and 49 nonmetallic industrial and 20 minor minerals. Their aggregate production in is about 550 million tonnes, contributed by over 3,100 mines (reporting mines) producing coal, lignite, limestone, iron ore, bauxite, copper, lead, zinc. More than 80 per cent of the mineral production comes from open cast mines and therefore, one must add the quantity of overburden to that of the mineral production in order to assess the total amount of annual excavation in India’s mining sector. The mining leases numbering 9,244 are spread over 21 States on about 13,000 mineral deposits occupying about 0.7 million hectares which is 0.21 per cent of the total land mass of the country. The aggregate value of the mineral production being more than Rs.450 billion (approximately $10 billion). The distribution of the value of mineral production shows that fuel minerals accounted for about 82% (of which solid fuels 44% and liquid /gaseous fuels is 38%), metallic minerals about 8%, non-metallic minerals 4% and the balance 6% is contributed by minor minerals.

 

KEYWORDS: Cement, limestone, local source, industry, blending and beneficiation

 


 

INTRODUCTION:

Mineral Policy opened the gates of Indian mineral industry to domestic and foreign investment, much of which was earlier reserved for the public sector. It aims to boost the country’s exploration and mining efforts and render the mineral industry more competitive1-5. The cement industry is one of the important contributors to Government exchequer. Excise duty collected by cement industry alone accounts for 5% of the total excise collection.6 Cement plays a very important role in the development of infrastructure and per capita consumption of cement is accepted as an important index of the country’s economic growth.

 

1. History of the cement industry in India

The history of the cement industry in India dates back to the 1889 when a Kolkata based company started manufacturing cement from Argillaceous. But the industry started getting the organized shape in the early 1900s. The first cement plant in India went into operation in Madras in 1904. In 1914, India Cement Company Ltd was established in Porbandar with a capacity of 10,000 tons and production of 1000 tons installed.

 

The World War I gave the first initial thrust to the cement industry in India and the industry started growing at a fast rate in terms of production, manufacturing units, and installed capacity. This stage was referred to as the Nascent Stage of Indian Cement Industry. In 1927, Concrete Association of India was set up to create public awareness on the utility of cement as well as to propagate cement consumption in India the cement industry dates back to the beginning of the present century. In 1936 most of the existing companies were amalgamated into associated cement company while there were 21 plants with a production of 3 million tones per year during the early first five year plan.7

 

Cement plays a very important role in the development of infrastructure and per capita consumption of cement is accepted as an important index of the country’s economic growth. Over the years since its inception in India in 1914, technology has developed8 and the country today has most of its capacity with the state of art technology. Skilled manpower development has also been rapid and the industry offers turnkey cement projects for cement production to countries abroad. Indian cement industry provides direct employment for around 70,000 people while creating indirect employment through process machinery manufacture, raw materials and other sources. It is estimated that one million tonne of cement production provides employment to around 50,000 persons downstream.

 

It is a capital-intensive industry, which means that competition is confined mainly to a small group of large industrial houses. The economic progress can be achieved by increasing the production coupled with improvement in the ways and means of productivity.9,10 This industry has recorded continuous growth since planning began. The Government has a complete control over the production, distribution and price of cement and this has dampened the growth of the cement industry.

 

In 1970, due to strict price and distribution controls, cement production became uneconomic and output stagnated. As a result there was a grave shortage of cement. To satisfy the demand, several producers started manufacturing PPC, blending in different pozzolanas, some suitable and some not so suitable.11

 

As a result several cases of unsatisfactory performance by PPC were reported. Consequently, the CPWD imposed a ban on use of blended cement for bridges that continues to be in force even today. Therefore, all the Government tenders specify use of only OPC. This obliges the cement industry in India to produce OPC, which increases green house emissions and reduces the potential available to the cement industry to utilize available fly ash and slag. There are several developments over the past few years in development and manufacture of blended cements in the country.12 Currently the blended cements are manufactured under strict quality control and meet international standards and the same compare favorably with OPC and in most cases offer far superior properties in different applications. As a result of this, BIS has approved blended cements and have incorporated them in the standards and they are widely used in all types of construction activities in the country by several construction industries.

 

India now has a per capita cement consumption of only   150kg. Skilled manpower development has also been rapid and the industry offers turnkey cement projects for cement production to countries a Over the period 2000-08, compound annual growth in cement consumption is noted at 7.2 per cent, some 3-4 percentage points higher than the long-term global average calculated over the past 20-30 years broad. Global cement trades are also showing signs of slowing. In 2006 total trade levels were measured at 180Mt, but by 2008 such trading volumes in cement and clinker were down to 164Mt. In brief, global cement consumption patterns are changing, with strong evidence of a slowdown emerging throughout 2008 with further sizeable declines in 2009, before a forecast rebound occurs in 2010.11

 

On the global scene, Indian cement industry ranks second only next to China in the cement producing countries of the World The quality of Indian cement matches with the World’s best. The current capacity of the cement industry is 151.2 Million Tones (MT),. (Large plants: 148.28 million tonnes. and Mini Cement Plants 11.10 mn.t.). The total cement production of a year is around 150 mn.t.

 

Though the cement industry has been in existence for over 9 decades, any appreciable growth could be witnessed only after the introduction of partial decontrol in 1982 culminating in total decontrol in 1989. The industry sustained a CAGR of 8% during the last decade. This would not have been possible, if the Government did not implement their liberalization policies. The industry also responded positively by adding capacities and increasing production continuously to meet the growing demand.10

 

2. Country Cement Production:

Cement Production in India:

The history of the cement industry in India dates back to the 1889 when a Kolkata-based company started manufacturing cement from Argillaceous. The cement industry in India saw the price and distribution control system in the year 1956, established to ensure fair price model for consumers as well as manufacturers. Later in 1977, government authorized new manufacturing units (as well as existing units going for capacity enhancement) to put a higher price tag for their products. A couple of years later, Government introduced a three-tier pricing system with different pricing on cement produced in high, medium and low cost plants.9

 

Cement industry, in any country, plays a major role in the growth of the nation. Cement industry in India was under full control and supervision of the government. However, it got relief at a large extent after the economic reform. But government interference, especially in the pricing, is still evident in India. In spite of being the second largest cement producer in the world, India falls in the list of lowest per capita consumption of cement. The reason behind this is the poor rural people who mostly live in mud huts and cannot afford to have the commodity. Despite the fact, the demand and supply of cement in India has grown up. In a fast developing economy like India, there is always large possibility of expansion of cement industry.13

 

3. Cement production and growth:

Domestic demand plays a major role in the fast growth of cement industry in India. In fact the domestic demand of cement has surpassed the economic growth rate of India. The cement consumption is expected to rise more than 22% by 2009-2010 from the consumption in 2007-08. In cement consumption, the state of Maharashtra leads with 12.18% consumption, followed by Uttar Pradesh. In terms of cement production, Andhra Pradesh leads with 14.72% of production, while Rajasthan remains at second position. The cement industry in India has contributed almost 8% to India's economic development.11

 

4. Investment Trends:

Cement and gypsum products have received cumulative foreign direct investment (FDI) of US$ 1708.69 million between April 2000 and March 2010, according to the Department of Industrial Policy and Promotion. Madras Cements Ltd is planning to invest US$ 178.4 million to increase the manufacturing capacity of its Ariyalur plant in Tamil Nadu to 4.5 MT from 2 MT by April 2011. In January 2010, rating agency Fitch predicted that the country will add about 50 million tonne cement capacity in 2010, taking the total to around 300 million tonne.

 

5. Future Scenario:

By the end of next Plan, cement production is expected to reach 300 mn.t. requiring an additional power of more than 2000 MW.

 

6. Research and Development (R and D):

Indian cement industry has capability to export to the extent of 15-20 mn.t. annually. Globalization leading to innovative methods of improving productivity and efficiencies through continued research is a compelling necessity and Indian cement industry has not fallen short.14

Following thrust areas have been identified for taking up specific projects:

􀂾 Upgrading by converting wet process plants to semi-dry and full dry process resulting in economies in fuel and power consumption.

 

Wet process capacity, which accounted for 97% in 1950, has been brought down to 3%

·        Co-processing of hazardous wastes in cement manufacture.

·        Processing of fly ash for enhanced use in cement/concrete.

·        Development of cements and binders based on nano-technology.

·        Improving the performance of size reduction operations.

·        Evaluation of technologies for co-generation of power from waste heat.

·        Adaptation of low NOx low SO2 technologies

·        CO2 absorption through Algal Farms.

·        Standardization of composite cement.

 

Arya (1983)15 studied technological and productivity changes for 15 cement manufacturing companies. Using data from annual reports of the companies for the years 1956-72 he estimates Cobb-Douglas production functions. The trend rates of growth show wide variation across his sample and fall in the range of 0.8% to 6.8% p.a. Capital intensity during that time period increases at an average rate of 2.8% p.a. for the sample group. Mehta (1980)16 also estimates Cobb Douglas production functions for some energy intensive industries including the cement industry. His sample period encompasses the years 1953 to 1965. He finds evidence of capital deepening in the production process but could not conclude any clear trend regarding efficiency improvements. Productivity in the cement sector for his time period grows at 6.1%.

 

7. Status of Limestone Availability:

Limestone is perhaps the most extensively exploited mineral gift of nature and the cement industry is the largest beneficiary of this mineral. Hence, the information on the latest status of availability of cement grade limestone is essential not only for entrepreneurs in making technological and financial decisions intending to set up green field cement plants but also helps planners in formulating the strategy for the growth of the cement industry. Although, many national and state level geological agencies have been exploring such deposits for different limestone based industries, it was only in the late sixties that serious attention was paid towards the assessment and exploration of cement grade limestone reserves in a more comprehensive manner keeping in view the potential for the growth and development of Indian cement industry. National Council for Cement and Building Materials (NCCB), the then Cement Research Institute of India, had taken up dating of the national inventory of cement grade limestone as a continued programmed project since 1974.12

 

Quality, quantity and minability of relevant natural raw materials are the three important determinants of economic viability if cement plant. In wider sense the preliminary assessment of these three determinants is the direct outcome of prospecting and this assessment provides the techno-economic basis of deciding to set up a cement plant. Moreover the aim of prospecting and exploration is to provide a minable reserve of usable raw materials sufficient to last for the economic life of a proposed plant. Naturally then the exploration works are internal to obtain the actual picture of a deposit by methods of successive approximation. An exploration turns out to be ideal when the difference between the forecast and actual date obtained during mining reduces to an acceptable minimum.

 

Any development that gets reflected in a mineral – based industry, like cement, involves substantial participation of capital, men and materials .Important aspect of this is the exploitation of minerals and rocks that go into the preparation of feed for cement kilns. The exploitation of these raw materials obviously depends on proper and effective execution of prospecting and exploration work planned for the deposits containing the raw materials. An exploration turns out to be ideal when the difference between the forecast and actual date obtained during mining reduces to an acceptable minimum.17,18

The prospecting and exploration being a fairly expensive operation, the quantum of work undertaken for a deposit is direct measure of the expenditure incurred on it.  In an industrial venture, therefore the prospecting and exploration works have to be optimized that the ultimate exploration of the deposit becomes feasible and remains profitable for the entire life of the plant with minimum expenditure on the initial and follow –up exploration.

 

In view of the importance  of prospecting and exploration work for setting up and  running a mineral based  manufacturing plant, and because of the  crucial financial implications and involvements, the need for a rationalized system of prospecting and exploration cannot be over – emphasized. The need is all the more justified for our country, where mineral exploration and when only a few of them have their own well laid system of planning, execution data collection, compilation and interpretation. This leaves a large amount of prospecting work unassisted due to the non-availability of any standard yardstick of comparison in this country. This non – uniformity, in many occasions, may lead to either risky ventures of developing inadequately explored deposits, neither of which is conducive for the economic growth   of the country.  This point assumes special significance in the context of cement industry, where large expansion is being planned involving a sizable investment on raw materials exploration to ensure a steady and dependable supply to the cement plants.

 

The present thinking in India is to nourish development of large cement plants with 2000 tpd capacity or more, as well as mini cement plants with less than 200 tpd capacities. In both the cases the pre- assessment of raw material quality has to be fairly accurate.  The large plants, in addition demand the quantitative estimates of raw materials to be highly reliable.  Therefore the further technology will demand a more realistic prognosis about quality and quantity of raw materials during exploration.

 

These considerations have led to the formulation of unified norms for prospecting, exploration and assessment of cement grade limestone deposits.  All the   provisions of the norms except for exploration method shall be equally applicable to deposits of calc-tuffia, kankar, calcareous sea sand and other carbonate deposits which may serve as the basic raw materials for cement industry.

 

In drawing up these norms an approach had been to group on the one land, all the limestone deposits of India, on the basis of their geological   and structural disposition, and to phase on the other, the prospecting and exploration works for different types of deposits. The   next step has been to indicate the pattern and programme of exploration of work including sampling for each phase and programme of exploration of work including sampling for each phase of exploration and each type of deposit.  In connection with this, mineral reserves have been categorized on the basis of their degree of reliability from very approximate to fairly accurate stage.  The nature and intensity of exploration work required for each phase of exploration and each type of deposits has been correlated with various categories of reserves.

 

8. CLASSIFICATION OF LIMESTONE DEPOSITS:

1. The limestone deposits of India may be classified into the following three types18.

a) Simple deposits

b) Complex deposits and

c) Intricate deposits.

 

This classification should be  based on the such parameters as the shape and extend of deposit, conditions lithologic and compositional variations geological age, structural disposition, topographic placement, tectonic features etc, which along with reserve estimates determine  the conditions and scale of  exploitation as well as the method and intensity of exploration. The broad pattern of exploration plan of a new deposit shall be worked out on the basis of its close similarity with any of the above  three types of deposits, however it may be noted that the classification   suggested above should  serve as a guideline for the estimation of the quantum pf exploration required.  There could be possible exceptions since the limestone deposits are result of long drawn natural processes which are varied and heterogeneous.  It is quite likely that a deposit may apparently seem to be simple / complex/ intricate, but may actually prove to be otherwise after further investigation.

 

Various known limestone deposits in India have been included into one or the other of the above three typed based on geological complexities (reflected in the mode of occurrence and morphological features) amenability to prospecting and proving operations as well as minability.

 

8.a. Simple deposits are large, continuous, bedded, horizontal to gently dipping undisturbed and uniform in quality such a Banku ( Shahabd and Wadi deposits of Lower Vindhyan (Bhima) age in Gulbarga  district  (Karnataka), Kajrahat deposit of Upper  Vindhyan age in Mirzapur district (UP), Ariyalur deposit of Cretaceous age in Trichirappalli district  (Tamil Nadu)  and Meliolitic limestones of Recent  to Sub –recent age in Saurashtra  district (Gujarat)

 

8.b.Complex deposits are:  (a) moderately to steepy dipping gently folded consistent (b) more or less simple but with frequent intercalations, variable thickness, detached uniform quality but with irregular shape and variable thickness (D) lenticular, folded or structurally disturbed.  A few  examples are Lanjiberna deposit of Archeanage (Gangpur Series) in Orissa, Mancherial deposit of Lower Vindhyan age in Adilabad district (Andhra Pradesh), Cherrapunji deposit  of Eocene age ( Jaintia series) in the Khasi Hills district ( Meghalaya) and  Lakheri deposit of Upper Vindhyan age ( Bhander Series) in Bundi district ( Rajasthan).

 

8.c .Intricate deposits include highly complicated, highly folded dislocated, irregular in shape or those deposits which are intensely interbedded, with clay or shale or show extremely varying form, thickness or assay values. A few examples are Ammasandra deposit of middle Dharwar age in Tumkur district (Karnataka), Khalari and Churi deposit of Archean age in Palamau district ( Bihar), Balasinor deposit of Lameta (Infra – trappeans) in kaira district ( Gujarat) and Malla limestone deposit of Pre- Tertiary age (ShaliSeries) in Ambala district ( Haryana).

 

9. CATEGORIZATION OF RESERVES:

Reliability of Different Categories of Reserves:

Specific bodies of limestone whose locations are, known, shall be termed as’ identified resources.  The deposits shall attain the status of reserves, with the first assessment of the extent and grade being made on the basis of reconnaissance prospecting.

 

Cement grade limestone reserves shall be prefixed with in of the qualifying expressions ‘ inferred’  “indicated” depending on the degree of reliability of the estimate and subject to mining  constrains in the following order18.

Identified Resources

Interred Reserve   - when Vg > 4% and Vr > 50%

Indicated Reserve – when   Vg > 3% Vr > 30%

Measured Reserve – when Vg> 1% and Vr > 10%

Where

Vg = anticipated deviation in CaO content from the actual value as mined, and

Vr = anticipated difference between the estimated and mineral reserves

 

Inferred Reserves shall mean in – situ geological reserves, Indicated reserves shall refer to the one calculated from random and scanty drilling substantiated by pitting and trenching.  Measured Reserves shall always refer to economically minable and recoverable reserve calculated from detailed grid drilling data or equivalent information on the deposit.  The quality of the mechanically minable reserve should be determined taking into account the recovery of care and sludge.

 

In addition to the above categories reserves, which shall be estimated during the different phase of prospecting and exploration, there shall be another category of reserve designed as “Developed Reserves” to be estimated only after the mining of a deposit has started.  Developed Reserves shall have = 0.5 percent and Vr = 0 to 5 percent.

 

In a working mine, the reserve should be periodically revised on the basis of feedback date from mining and proving operations.

·        Inferred reserve shall be used for the purposes of fling applications for a prospecting license.

·        Indicated and measured reserves shall be used for the purposes of filing applications for mining lease.

Indicated and measured reserves shall together be used for preparing project reports, taking financial decisions for setting up of a cement plant, and for the capital involved on quarrying.

 

A per requisite for setting up of a new rotary kiln plant shall be to ensure that the measured reserve is enough for at least 30 years together with sufficient recoverable quantity of  indicated  reserve for at least 15 years. In addition there shall be an equal quantity of indicated reserves for future expansion purposes.

 

The requirement of measured reserve that is the economically proven reserve for a rotary kiln plant shall be calculated on the basis of its capacity, taking into account the mining losses (15%) and shortfall due to reserve estimation errors(15%)amounting to approximately 30%of the actual limestone requirement. The requirement of indicated reserve from which the recoverable quantity for an additional life of fifteen years is to be made available shall be calculated by multiplying the fifteen years measured reserve as mentioned above by a factor of 1.5.

 

In calculating the reserves, the consumption of lime stone may be assumed as 1.5 tonnes per tonne of clinker and the number of working days in a year as 300 based on the above correlation the reserves may be calculated by using the following simplified equation

R ms =   18   x    103

Rind =0.75 x R ms

R ms = measured reserve

C=daily production capacity of a plant and

Rind= indicated reserve

Rounding off of the figures obtained on the basis of the above procedure, the required (tentative) reserves for new rotary kiln plants of various capacities may be taken as indicate.

 

10. RESERVE ESTIMATION:

Methods of Reserve Estimation19:- Limestone reserve shall be calculated by the  following methods depending upon their applicability:

a)        Geological factor and area:

b)        Average  factor and area;

c)        Geological or mining block

d)        Polygon, triangle / or rectangle;

e)        Contour /isoline / isopach / isochore, and

f)        Combination of the above methods.

 

Reserve Estimation in Different phases:

In the Reconnaissance Prospecting Phase the overall minable reserve of the deposit or property may be expressed by the formula

Q = Vd = Smd

Where Q = the reserve in tones, V = the volume of the deposit, in m2, D = the average bulk weight of the mineral, in tones per m3, S = the projection area of the deposit or part of it within the boundary of the area for reserve calculation, and M = the average thickness of the deposit along the line normal to the projection plane.

During detailed prospecting, and exploration a d proving stages, reserves shall be calculated with appropriate consideration of the utility factor.  Here the minable reserve shall be calculated and expressed by the formula;

Qm= Q1 – (Q2+Q3)

Where Qm = actual minable reserve, Q1 = total reserve in the entire property

Q2 = reserve which is not minable due to several reasons, and

Q3 = the quantity of voids and bands of gangue rocks in the limestone

Some Basic Parameters for Reserve Estimation

 

During  Phase II ( Detailed Prospecting) and  Phase III ( Exploration and Proving), reserve shall be calculated according to horizons or customary bench levels  , discrete mining blocks and sections, and shall be shown along with the computed grades for each of these blocks or sections in each of the horizons or benches.

 

The reserves shall be grouped under different intervals of limestone to overburden ratio, or limestone to waste ratio, which will give the idea of economic limitations of such calculated reserves at the actual exploration m stage. The reserve shall take into account t the recovery factors and presence of larger voids and cavities if they are common in the deposit.  If a part of the reserve is under the water table, its minability should be determined with respect to the cast and availability f regular pumping arrangements. Calculation of reserve shall take into consideration the mine laws, rules and regulations, the working limits from the lease boundary, loss of available reserve.

 

The depth of exploration and reserve   estimation should generally be limited to 30 to 40 m from the surface up to certain level depending on the physiographic and other factors.

 

11. DESIRABLE PHYSICAL, CHEMICAL AND MINERALOGICAL CHARACTERISTICS:

Some of the desirable physical, chemical   and mineralogical properties of cement grade limestone are:

a)      The average grain size of calcite in cement grade limestone should be preferably be below 0.25 mm, as the grain size has a definite relation with the burnability of limestone.

b)      The presence of coarse grains of quartz or silicious veins is undesirable as it may affect the grindability and burnability of limestone.

c)      Chloride content should not exceed 0.05 percent as it would otherwise cause corrosion and other process difficulties, especially in dry process cement manufacture.

d)      The presence of sulphur particularly in sulphate state is undesirable as the decomposition of the sulphate phase is difficult.

e)      Limestone should have low natural moisture content (less than 5 percentage preferably below

f)       Limestone should have low compressive strength preferably below 1000 kg/cm2

 

12. DETAILS OF ANALYSIS AND TESTS:-

Technological assessment of limestone shall consist of the following tests and a composite sample shall be prepared from individual samples characterizing the approximate customary bench height and shall be analyzed for SiO2, Al2O3, SiO2 and LOI. This phase of chemical analysis is intended to help in raw mix calculations. If total sulphur is found to be more than 0.6 %, the sulphates and sulphide state of sulphur shall be determined 18

Chemical analysis

Mineralogical and petrographic analysis and

Physico mechanical tests

Chemical analysis

All individual samples collected in the field shall be analyzed for any one of the following

(i)  CaO+MgO+CO2

(ii) CaO + MgO+   insoluble residue in Hcl

If the total of the above seven components in the combined samples of carbonate rocks does not exceed 98.5%, P2O5, Na2O, K2O shall be additionally determined.

 

Complete chemical analysis of cement grade limestone shall, therefore refer to the determination of CaO, MgO , SiO2, Al2O3,SOand LOI, Fe2O3 ,Mn2 O3 K2O , Na2O, P2 05, SO3,Cl and LOI. The number of composite to be analyzed for complete chemical analysis in each phase of exploration should be decided separately in each individual case.

 

Cement grade limestone resources should be identified on the basis of the above composition having been determined at least for a few selected samples. Table 2

 

12.a. CONTROL ANALYSIS18 – Ten percent of the sample chemically analyzed should be subjected to repeat analysis under secret coding with double HF treatment method to be adopted for some of them.  The difference between the two results should be preferably by within the permissible limit

 

12. b. PHYSICO - MECHANICAL TESTS:

The Physico -Mechanical tests18 shall refer to the determination of the following parameters:

Colour and fracture of limestone – shall be determined in hand specimens drawn from lump samples.  All the visible variations should be described.

Apparent density – shall refer to the weight of unit volume of an absolutely dry limestone   and shall be done on 40-50 samples from different parts of the deposit.

Bulk weight –.  It shall be determined on minimum 40-50 samples from different parts of the deposit.

Porosity of limestone – shall refer too the ratio, expressed as a percentage of the aggregate volume of the pore space and the total volume of the rock.

It may either be experimentally determined or calculated by the formula:

P= (1- d/y) x 100 %              …..           ….

Where   P = porosity, d = bulk density, and y = theoretical density of the rock

·        Natural moisture content - shall be determined from the weight of the rocks in natural state and after drying at + 110c with the help of the formula:

Wn = W’ – W” x 100%

              W’

Where W n= natural moisture content, W’ = weight of the rock in natural state, and

W” = weight of the rock after drying.

Moisture content shall be determined for as many samples, as practicable for both natural and water immersed limestone, depending on extent and hydrological conditions.

·        Looseness factor (K1) – shall refer to the ratio of the volume of loosened rock (V1) to its volume in a pillar  (V p ):

K1 =   V1 /   V p

Looseness factor shall be determined by digging test pits   2 x 2 x 2 m in size at 400 m interval along strike and accurately measuring the volume of excavated rock.

Hardness of limestone – shall be expressed in Mohr’s scale.

Strength of limestone – shall refer to the compressive strength determined in the conventional way on cubes of 5 cm edge length, both in dry and wet samples.

 


 

Table1: BROAD CHEMICAL SPECIFICATION CEMENT GRADE RUN–OF-MINE    LIMESTONE

OXIDE COMPONENTS

ACCEPTABLE RANGE FOR MANUFACTURE OF ORIDNARY PORTLAND CEMENT

LIMITNG VALVES TAKING INTO CONSIDERATION OTHER TYPES OF CEMENT, SCOPE OF BENEFICATION AND BLENDING

 

Percentage

Percentage

Cao

44-52

Min 40

Mgo

Max 3.5

Max  5

SiO2

 

To satisfy the LSF and  silica modulus of the mix

Al2O3

Fe2O3

Mn2 O3

<0.5

<3

R2O (K2 O + Na2 O)

<0.6

<1

Total S as SO3

<0.6

<0.8

P2 05

<0.6

<1

Cl-

<0.05

<0.1

 

Table2: PERMISSIBLE DIFFERENCES IN CHEMICAL ANALYSIS OF COMPONENTS

Raw Material

PERMISSIBLE DIFFERENCE IN WEIGHT PERCENT

 

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

LOI

Pure

lime stone

0.20

0.10

0.10

0.50`

0.20

0.04

0.5

Impure limestone

0.50

0.30

0.15

0.40

0.20

0.04

0.5

CourtesyNORMS FOR PROVING LIMESTONE DEPOSIT FOR   CEMENT MANUFACTURE, DIRECTIVE PROVISIONS, CEMENT RESEARCH INSTITUTE OF INDIA p.18

 


Crushability of limestone – shall represent a generalized parameter including elastic, plastic and strength properties and shall express the energy consumed in crushing the rock under a dynamic load. The work index W.I is calculated from the average of 10 breaks using the formula.

W I = 2.59 / c / y

Where C = impact crushing strength, and

Y = specific gravity.

Grind ability of limestone – shall refer to its amenability to fine size reduction and    shall be expressed as Bond’s index.

 

12.C .RECORDING AND   REPORTING OF DATA

Recording of Data18 – The recording of data shall include the following.

a)      Maintaining the field diary by the exploration of geologists.

b)      Maintaining  the record of sampling  during the period of exploration and

c)      Documentation of analysis results and deposit characteristics.

The field diary of the exploration geologists should   contain exhaustive details of field observations with on the spot sketches of natural sections litho logical variations   joint patterns and all other geological and structural features of importance.

 

The record of sampling at all phase of exploration should be accurately maintained in the proposed  proforma   I and  II   as   indicated in the norms prescribed .by CRI.

Reporting of Data Exploration data shall be presented in two types of reports

a)      Interim Assessment Report and

b)      Techno – economic Report.

Interim assessment report shall pertain to Phase and II.  It shall be necessary for planning the subsequent phase of exploration programmes as well as for taking interim actions on prospecting license or mining   lease.

 

13. Utilization of Marginal Grade Limestone

As per the estimates, about 32632 mn.t  (33.5%) of the total 97430 mn.t of limestone reserves are of marginal grade  in India In addition, due to the poor and variable coal quality with high ash content, even a part of the cement grade limestone is turning to be marginal grade for cement manufacture. Since the available cement grade limestone reserves are not going to last forever, utilization of marginal grade limestone must be given immediate attention and priority through development of suitable techniques. Marginal grade limestone can be utilized for cement manufacture through any of the following techniques:14

􀂾 Computer aided deposit evaluation and mine planning for rational/optimal utilization of different grades of limestone through selective mining and blending.

􀂾 Use of sweetener which could be high grade limestone or industrial wastes like lime sludge etc.

􀂾 Modifications in raw mix design and process parameters and use of mineralizes.

􀂃 Use of low ash fuels, such as Pet coke etc.

􀂃 Use of natural gas as fuel.

􀂃 Manufacture of low CaO reactive belite and other special cements.

􀂃 Up gradation of limestone quality through dry beneficiation techniques.

The excessive use of sweetener is already affecting the economic viability of a number of cement plants. NCB has been carrying out detailed studies to determine the suitability of Indian limestones to different techniques of beneficiation including the relatively conventional differential grinding and Sieving techniques (DGS) as well as non-conventional techniques like Electrostatic Separation (ESS), Optical Sorting and Bacterial Leaching.

 

14. Incentive for Using Low Grade Limestone, Industrial and Mining

14.a. Wastes: Technologies for use of marginal grade limestone, including limestone with high silica, magnesia or alkalis need perfection on a mission mode, their promotion on large scale need suitable incentives to the cement plants. A lower rate of royalty may be fixed for utilizing low grade20 (high silica / high magnesia) limestone and calcareous shale.

 

14.b. Periodic Re-assessment of Limestone Reserves: In order to ensure the availability of various grades of residual limestone reserves for rational utilization, periodic re-assessment of captive limestone mines of all cement plants should be carried out by an independent agency such as NCB or IBM.  The state DMG’s (Departments of Mines and Geology) may be advised to incorporate the activity of proving of cement grade limestone deposits in their annual field program

 

Cement plants in India utilized about 20% of fly ash generated by thermal power plants and almost all the granulated slag generated by steel plants as compared to almost 100% fly ash and 84% of granulated slag utilized by the Japanese cement industry.

 

·        In India the extant quality standards allow manufacturing of cement by blending with either fly ash or slag only. Manufacturing of cement using   more than one waste is not allowed in India in view of absence of quality standards permitting the same.

Use of Alternate Fuels14

·        Use of hazardous and refuse derived combustibles and municipal solid waste as fuel is common in countries like Canada, EU, Japan and Korea, but regulations do not yet permit such use in India.

·        CPCB is actively engaged in plant level trials in respect of wastes such as shredded tyres, refinery sludge, paint sludge, Effluent Treatment Plant sludge and Toluene Di-Isocyanite tar   waste, and in formulation of guidelines for use of these wastes as fuel by cement industry. A notification allowing the use of   these wastes is expected shortly.

Ministry of Environment and Forests (MoEF) had been formulating guidelines for:

Implementing the principle of ‘Polluter to Pay’ for disposal of wastes.

·        Treatment, storage and disposal facilities for cost effective co processing of combustible industrial wastes in cement kilns as an alternative to  incineration.

·        Restricting land filling of hazardous and toxic combustible wastes.

·        Having potential for co-processing in cement kilns.

·        Duty free import of pollution control and energy efficiency improving

Excise duty should be to a considerable level on clinker produced through co processing   of hazardous wastes and bio-fuels, subject to a minimum of 20% replacement of conventional fuel.

 

By using blended cements, cement industry supports the cause of sustainable development by way of reducing the green house gases into the atmosphere 21,22and also reduces the menace of the huge quantity of fly ash and slag generated by other industries. Therefore it is desirable that Government takes a concerted view and lifts and the ban on the use of PPC and other blended cements in the public tenders and incorporates necessary amendments in the cement specification provided in the tenders. The poorer quality lime stones can be made useful for manufacture of second grade cement by suitable blending and beneficiation techniques. The concept of raw material requirement  for cement making are  being continuously changed 23-30 It is pertinent to think of using low grade limestone high in magnesia content available for manufacture of second grade cement which has slightly inferior properties available. M.P. Srivatsava et al, 31 have recommended that the techno economics of low silica limestone vis-à-vis indigenously available limestone should be worked out   with special reference to utility in SAIL Mines.

 

A thorough research to explore the possibility of adopting developed techniques on certain relatively impure deposits would enhance the limestone utility level in industries to a greater extent.

 

Views expressed are truly of the author not of the organization to which the author belongs.

 

ACKNOWLEDGEMENT:

The Author expresses her sincere gratitude to the Commissioner, Department of Geology and Mining, Dr. P. Periakali, Professor and Head (Retired), Department of Applied Geology, Dr. K. Ravichandran, Reader, Department of Analytical chemistry, University of Madras and Dr. S. Thangadurai , Lecturer, Raja Doraisingam Government Arts College, Sivagangai  for their encouragement in presenting this article.

 

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Received on 22.10.2010        Modified on 18.01.2011

Accepted on 07.02.2011        © AJRC All right reserved

Asian J. Research Chem. 4(4): April, 2011; Page 516-523