Introduction

The project “Energy-effective production of lime products”

aims to predict the thermal behavior and degeneration of lime-

stones and dolomites when calcinated to lime and dolime. The

project consist of three parts: 1) Explain the causes of thermal

deterioration, 2) Develop methods for prediction and 3) Imple-

mentation of the results to the industry. This report is a part of

the third stage, describing and comparing an implementation

attempt with the methods used in laboratory scale.

Geology of Gotland

The Gotland bedrock consists of limestone, marlstone and

sandstone geographically distributed according to Figure 1.

The bedrock is predominately from the early to mid-Silurian

period about 430 million years ago when the Baltic Sea was a

shallow tropical sea located close to the Equator (Erlström et al

2009). The Silurian strata of the island have its oldest parts in

the NW and the youngest in the S and have not been subjected

to any greater compaction or heating. The strike of the sedi-

mentary limestone is dominantly northeast/southwest and the

limestone dips to the southeast (0.15˚- 0.3˚; Erlström et al

2009).

The Stucks area is situated in the northernmost part of Got-

land (Fig. 1). Here, pure limestones dominate, marls occur on

the surface only as minor pockets. The limestone has a general

thickness of ca 30 – 50 m, below is marls and marly lime-

stones. Quarrying in the area has a long history, beginning in

the early 1900‟s. In 1997 SMA Mineral AB re-opened the

quarry as a part of a lime kiln purchase in Oxelösund. The

quarry has been steadily increasing its volumes and is now

mining ca 1 million tons of high purity limestone every year.

The limestone is divided into crinoid limestone, fragmeneted

limestone, reef limestone and stromatoporoid limestone. Frag-

mented limestones and crinoid limestones usually form the

base for the development of the reef limestone (cf. Fig 2). Reef

limestones are build-ups of reef forming organisms, in this case

corals and stromatoporoids (a sponge that was the dominant

reef-building organism during the Silurian period). This reef

build-up is flanked by debris in the form of crinoid limestones

and fragmented limestones. On the top, a layered build-up of

stromatoporoids forms the stromatoporoid limestone (Fig 2).

Energy effective production of lime products – comparing industrial and scien-

tific laboratory methods for prediction.

By Olof Sandström, PhD

Olof Sandström, Graptolit Geoproject AB, Kapellgatan 10, SE-214 21 Malmö, Sweden. olof@graptolitgeo.se.

Fig. 1. Map of Gotland with the distribution of the

main lithological facies (from Sandström 1998). The

photograph shows the area of Stucks limestone

deposit and quarry.

Fig. 2. A generalized facies model for the most com-

mon lithostratigraphic succession on northern Got-

land. The thickness of such a unit varies between

15m and 60 m.

Fig. 3. Geologic profile, chemistry and thermal re-

sults of the two methods of DH 1. The letters a – j

refers to example photographs of different facies in

Fig 4. Thickness of the right hand side of the litho-

logical column refers to the system by Dunham

(1962) and the letters at the bottom of the column

are: m= mudstone; w=wackestone; p=packstone;

g=grainstone; b=boundstone.

Methods

Limestone classification follows Dunham (1962) and the no-

menclature used for this project (marl, crinoid limestone, frag-

meneted limestone, reef limestone and stromatoporoid lime-

stone).

For the project a laboratory scale kiln was built at Lund Uni-

versity, and a method for measuring the thermal detoriation was

developed. This method is however not really applicable for a

large sample size with high throughput. A method developed

by SMA Mineral AB can use coarse +1cm fractioned limestone

with faster throughput, since more samples per time unit can be

handled. The question is whether the two methods are compara-

ble, and whether they yield similar results. In an attempt to im-

plement and model the Stucks reserve for thermal detoriation a

comparative test was made on two selected drill cores from the

area. The method developed by Lund University will here be

referred as the Lund-method and the method developed by

SMA Mineral AB will be referred as the SMA-method.

The SMA-method.

Approximately 2 kg limestone is crushed in a jaw crusher with

CSS=1cm. The sample is sieved on 5mm and 10mm. 500g

(±0,1g) of the 5/10 fraction with equal over and under- size

portion, is placed in a ceramic bowl and heated with an even

increase to 1150°C in 240 minutes. 1150°C should be reached

within 60 minutes. After 240 minutes, the kiln is shut off and

the sample is slowly cooling down until it is cool enough to be

Fig. 4. Photographs showing the different facies of DH 1. The position of each picture is indicated by its corresponding letter in Fig. 3. a. Crinoid limestone

(grainstone) with abundant stylolites. b. Fragmented limestone (packstone). c. Stromatoporoid limestone (boundstone) intercalated with fragmented limestone

(packstone). d. Reefal fragmented limestone (packstone). e. Stromatoporoid limestone (boundstone). f. Crinoid limestone, partly with micritic matrix (packstone/

grainstone). g. Fragmented limestone with solitary rugose corals and coated grains (wackestone/packstone). h. Reef limestone (boundstone), partly rich in stro-

matoporoids. i. Crinoid limestone with abundant stylolites and fine clay intercalations (grainstone). j. Fragmented marly limestone, with abundant fossil frag-

ments and in part rich in crinoids (storm depositions; packstone).

placed in an exicator.

The entire sample is weighted (m1). Then it is carefully

sieved by hand on a 5mm sieve. All of the sample on the sieve

must be in contact with the sieve-cloth. Weigh the +5mm sam-

ple (m2). The thermal detoriation is then the percentual differ-

ence between the two weighted samples:

% thermal detoriation =

The Lund-method

A core sample is weighted (m1) and then placed in a ceramic

furnace and slowly heated to 1050°C. The top temperature is

held for 4 hours and is the cooled down slowly. When the tem-

perature of the sample cooled enough to be managed it is

placed in a sealed container to avoid moisture and CO2 expo-

sure.

The sample is removed from the container and placed in a

vibratory sieve shaker with 8, 4 and 2 mm sieves. The sample

is shaken for 1 minute with amp.=2,5 and after that for 2

minutes with amp.=1,5. Before burning, after burning and after

each shake the number of pieces larger than 8mm are counted.

Before sieving, each sieve is weighted separately. After the last

sieving procedure, each sieve with material is weighted and

the actual sieve weight is deducted (m8mm, m4mm, m2mm). The

total amount of fines is the sum of material that has passed the

8mm sieve.

% thermal detoriation =

Shatter tests

The shatter test is a standard way to test thermal detoriation in

kilns and is used by kiln manufacturers to test whether their

kiln is suitable for the intended material or not. There are sever-

al varieties and each manufacturer has their own version of the

method. The problem with these methods is that they do not

Fig. 5. Geologic profile, chemistry and thermal

results of the two methods of DH 2. The letters a – i

refers to example photographs of different facies in

Fig 6. Thickness of the right hand side of the litho-

logical column refers to the system by Dunham

(1962) and the letters at the bottom of the column

are: m= mudstone; w=wackestone; p=packstone;

g=grainstone; b=boundstone.

seem to be too reliable. If the method says OK, then it is OK,

but when the method says not OK, it is still OK in about half of

the cases according to my own experience. Another problem is

that they require relatively large sample size. I will give a gen-

eral description of how shatter tests are made.

From the sample one or more cubes are cut, normally about

1dm3 each. The cubes are weighted, placed in a furnace and

heated to a temperature suitable for the kiln per see. After the

heating process, the cube(s) are placed in a tumbler or shaker

and „mishandled‟ for some time. After tumbling process, the

material is sieved and each fraction is weighted. Depending on

manufacturer and type of use, different sieves sizes are used.

Results from shatter tests are to some extent comparable to

the methods tested in this report. However, shatter tests are

normally much more expensive, and are suitable for very few

samples to test the kilns suitability for a certain finding. The

method is not suitable for quantification and very large amount

of samples.

Results

Two drillcores DH1 and DH 2 was selected for a detailed

examination. They were described geologically and samples

were taken for analysis of thermal detoriation in the Lund la-

boratory. Already jaw-crushed material from a previous chemi-

cal test was available and was used for the SMA-method. This

material was collected in 2m intervals.

DH 1 (fig 3) is 40,97 m deep. It begins with a marly frag-

meneted limestone (packstone; Fig 4j) partly rich in crinoids

followed by a stylolite-rich crinoid limestone (grainstone; Fig

4i), a reef limestone with abundant stromatoporoids

(boundstone; Fig 4h), a fragmented limestone, with finegrained

Fig. 6. Photographs showing the different facies of DH 2. The position of each picture is indicated by its corresponding letter in Fig. 5. a. Stylolite-rich crinoid

limestone (grainstone). b. Crinoid limestone with fine clay intercalations (grainstone). c. Crinoid limestone (partly fragmented limestone) rich in stylolites

(packstone/grainstone). d. Fine-grained limestone, partly fragmented limestone (wackestone). e. Reef limestone (boundstone). f. Fragmenetd limestone with

micritic matrix, partly rich in crinoids (wackestone/packstone). g. Coarse crinoid limestone rich in stylolites (grainstone). h. Fragmeneted limestone rich in cri-

noids and stylolites (storm layer; packstone). i. Nodular marl with intercalations of storm deposited fragmented limestone (wackestone/packstone).

matrix and partly abundant in solitary rugose corals

(wackestone/packstone; Fig 4g), a crinoid limestone with partly

micritic matrix (packstone/grainstone; Fig 4f), Fragmented

limestones (packstones, Fig 4b, d) intercalated with stromato-

poroid limestones (boundstones; Fig 4c, e). On top is a crinoid

limestone with abundant stylolites (grainstone; Fig 4a). CaO

and SiO2 values follow the micritic content (i.e. Dunham clas-

sification), more micrite gives higher SiO2 and lower CaO (cf.

Fig 3 Dunham classification and the chemical curves). The %

fines curves from the two methods look somewhat different.

This is because of sampling interval. About 4 times denser

sampling interval for the Lund-method compared to the SMA-

method yields a more spiky looking curve for the Lund data. If,

however you look at the more large-scaled cyclicity of the

Lund data, one can see that there is a correlation.

DH 2 (Fig 5) is exactly 40m deep. This sequence begins with

nodular marl that coarsens upwards to a fragmented limestone

with a high degree of micritic matrix (mudstone/wackestone/

packstone; Fig 6i, h). This is followed by a crinoid limestone

rich in stylolites (grainstone; Fig 6g), a fragmented limestone,

partly crinoid-rich (wackestone/packstone; Fig 6f), a reef lime-

stone (boundstone; Fig 6e), a finegrained limestone, partly

fragmental (wackestone; Fig 6d), a fragmented limestone with

minor stylolites (wackestone/packstone; Fig 6c), and ending

with a stylolite-rich crinoid limestone (packstone/grainstone;

Fig 6a, b, c). Here too, the CaO and SiO2 curves seem to follow

the micritic content, although it is not as obvious as in DH 1.

Also, the two % fines-curves show the same pattern and gen-

eral similarities as for the DH 1.

Fig. 7. Comparision of the result from DH 2 of the two methods. Black curve

is the result from the Lund-method with a moving average of 4. Gray curve is

the result from the SMA-method. The curves generally follows the same

pattern and with similar magnitude.

Fig. 8. Comparision of the result from DH of the two methods. Here the aver-

age of each 2 m interval of the Lund-method (black curve) is compared with

the SMA-method (gray curve) The result from this comparision show that the

methods are probably comparable, with very similar outcome.

Correlating the methods

In order to see how good the two methods correlate, the two

curves from the DH 2 was compared. In order to smoothen the

Lund-data a moving average filter was applied with a four sam-

ple mean. This smoothens the curve a bit and dampens the vari-

ation. Comparing the two curves in the same diagram shows a

very good general correlation between the two (Fig 7). A se-

cond way to check the correlation of the two is to make fewer

samples of the Lund-method by averaging every 2 meters. This

gives a very smooth curve, almost identical with the curve from

the SMA-method (Fig 8).

Discussion and Conclusions

The two methods seem to correlate well with each other,

making the SMA-method a good choice for further industrial

testing and modeling. In an older report from SMA (Gräsberg

unpublished), correlation between shatter tests and the SMA-

method was proven. However, the shatter test showed generally

higher values compared to the SMA-method.

In previous case studies from the project (Sandström, 2011) a

good correlation between lithology type and thermal detoria-

tion was evident. However, here it is not the case. Looking at

the data, there seem to be a weak negative correlation to SiO2-

content and a weak positive correlation to stylolite frequency.

Hatched areas in Fig 8 shows where stylolites are abundant. A

third alternative is microfacies and micritic content that may

correlate as well. Looking at figures 3 and 5 a correspondence

between grainstone and increase in thermal detoriation is possi-

ble.

Sandström & Calner (2011) shows in an example from the

same area the importance of deep geological knowledge in or-

der to find, plan and produce correct qualities of limestone.

Here a systematic approach is used that has been developed by

Thomas Aigner (eg. Pawellek & Aigner 2004), called

“Dynamic Stratigraphy” and involves a systematic analysis of

rock sequences along a hierarchy of spatial and temporal scales

from microfacies analysis to larger scaled sequence- and stack-

ing analysis. Correct knowledge of the mechanisms behind the

thermal behavior is of essence for the dynamic understanding

of the relation between depositional environment, tectonics and

burial history if the carbonate rock.

The good correlation between the two methods does, howev-

er mean that one is able to model and selectively quarry on

thermal quality even when the background knowledge is lim-

ited. However, one will need to use denser sampling and a

denser array of drillings to get good accuracy in the model.

With a good knowledge on the causes of thermal detoriation

one can make correct correlations to other parameters (such as

chemistry, lithology or texture), and obtain a good precision

with less laboratory work. One example of this is the case-

model presented in Sandström (2011).

References Dunham, R.J., 1962: Classification of carbonate rocks accord-

ing to depositional texture. In W.E. Ham (ed.): Classifica-

tion of carbonate rocks, 108–121. American Association of

Petroleum Geologists, Memoir 1.

Erlström, M., Persson, L., Sivhed, U. & Wickström, L., 2009:

Beskrivning till regional berggrundskarta över Gotlands län.

SGU serie K 221, 66pp.

Pawellek, T. & Aigner, T., 2004: Dynamic stratigraphy as a

tool in economic mineral exploration: ultra-pure limestones

(Upper Jurassic, SW Germany). Marine and Petroleum

Geology 21, 499-516.

Sandström, O., 1998: Sediments and stromatoporoid mor-

photypes in Ludfordian (Upper Silurian) reefal sea stacks

on Gotland, Sweden. GFF 120, 365–371.

Sandström, O., 2011 (in press): Energy-effective production of

lime products – Case models. MinFo Publications no. xxxx,

xxpp.

Sandström, O. & Calner, M., 2011 (in ms): A model for north-

ern Gotland high purity limestones based on a Dynamic

Strati-graphic concept . MinFo Publications no xxx, xxpp.