Reliable Analysis of Sulfur and Carbon in Limestone, Dolomite and Lime

Limestone and dolomite are sedimentary rocks with an enormous variety of applications across an extensive range of fields. Limestone is commonly used as raw construction material, fluxing agent, animal feed filler, aggregate and acid neutralizing agent.

When calcined, burnt lime (CaO) is produced, which is more suitable for use in acid-neutralization and as a construction material. Dolomite is considered to be superior to limestone as a construction material due to its hardness.

Quality- and process-control demand rapid and accurate analysis of the carbon and sulfur content in cast iron and other casted products. This article demonstrates the speed, simplicity and reliability of carbon and sulfur detection using the G4 ICARUS Series 2 equipped with a high-frequency (HF) induction furnace.

Measuring Principle

Combustion occurs within a sealed HF induction furnace under a flow of oxygen. While the sample, with the addition of a metallic accelerator, is heated by induction. Combustion takes place at temperatures over 2000 °C.

Sulfur compounds are then oxidized to SO2 and carbon to CO2. Subsequently, the total amount of carbon and sulfur elements are calculated in relation to the amount of these combustion gases, which are quantified using selective detection systems.

Combustion Without Compromises: G4 ICARUS

With its robust HF-furnace supplemented with ZoneProtect™, its novel vacuum-free automatic cleaning system, HighSense™ detectors and electronic flow- and pressure-control, the G4 ICARUS Series 2 is a smart choice for every industrial user who demands a reliable instrument, even in extreme conditions.

The G4 ICARUS Series 2 has the capacity to rapidly measure both carbon and sulfur in cast iron and related materials with excellent accuracy – usually less than one minute.

Reliable Analysis of Sulfur and Carbon in Limestone, Dolomite and Lime

Image Credit: Bruker AXS Inc.

Sample Preparation

For the highest precision, the sample should be ground or crushed into a uniform powder before analysis takes place. If applicable, the sample should be dried for a minimum of 1 hour at 110 °C. No additional sample preparation is necessary.

Method Parameters

  • Accelerators:
    • Tungsten/Tin: ~1.5 g
    • High purity iron chips: ~0.7 g
  • Analysis time 1: 35 seconds (power Level: 4)
  • Analysis time 2: 25 seconds (power level: 0)
  • Baseline check before analysis: 5 seconds
  • Baseline check after analysis: 5 seconds
  • Crucible cool time: 10 seconds
  • Purge time: 5 seconds
  • Sample mass: ~0.2 g (weighed to 0.1 mg)
  • Start delay: 5 seconds 

Calibration  

The calibration of the analyzer is completed using reference materials with certified concentrations of carbon and sulfur. The analysis software supports multi-point calibration with multiple CRMs and single point calibration with one CRM. 

Procedure  

I. Determination of the Blank Value  

Conduct at least three analysis runs of the blank value by introducing the described number of accelerators into a preheated1 crucible and analyze. 

II. Measuring Reference Materials  

  • Select CRMs for calibration and identify them using the certified concentrations in the analysis software with designation.
  • Weigh the necessary amount of reference material into a preheated1 crucible, and carry the exact mass into the analysis software. Conceal the material with the desired amount of accelerator and run the analysis.
  • For each reference material used, repeat step 2 at least three times. Calibrate the analyzer with the blank values recorded under I. and the results acquired with reference materials II. (for further details, refer to the user manual). 

III. Sample Measurement  

  • Weigh ~0.2 g of sample into a preheated1 crucible and transfer a precise amount of the sample mass to the analysis software. Conceal the sample using the described amount of accelerator and run the analysis.
  • Repeat step 1 until a suitable amount of repetitions has been achieved. 

Calibration Example  

Concentration levels for total carbon and total sulfur in limestone and dolomite are typically in the range of Carbon: 10 - 15% and Sulfur: 0.02 - 0.4%, whereas the contents found in burnt lime are typically Carbon: 0.1 - 2% and Sulfur: 0.01- 0.25%. 

The typical concentration range is beneficial information to consider when selecting suitable reference material for calibration. While all detectors are linearized, and an extrapolation of the calibration curve is feasible, it makes for good laboratory practice to ensure that all samples are within the calibrated range. 

For this article, the calibration and method are the same as that used for cement in Lab Report CS/ONH 020. The resulting calibration for carbon and sulfur produces a R2 = 0.9999, which clearly demonstrates the outstanding accuracy, linearity and reproducibility of the G4 ICARUS Series 2 detection system and the method as a whole. 

Notes:  

1For optimal precision, ceramic crucibles should be pre-heated in a muffle furnace at ≥1250 °C for at least 15 minutes or ≥1000 °C for a minimum of 2 hours. To prevent contamination, crucibles should be carefully handled with clean tongs and transferred to a desiccator for storage.

Table 1. Used reference materials. Source: Bruker AXS Inc.

Standard (lot#) Material Total carbon / % Total sulfur / %
AR 4006 (411B) ore 4.19 4.07
AR 4007 (1212E) ore 7.27 3.26
AR 4012 (52199) limestone 11.97 0.044
EZRM B 483-1 cast iron 2.46 0.103
Ag2SO4 (p.a.) pure substance n.a. 10.12 – 10.28
(98.5 - 100% purity)

 

Results  

The reproducibility of the G4 ICARUS Series 2 and the method detailed is determined by a sequence of 10 repetitive measurements of real production samples. 

Table 2. Dolomite. Source: Bruker AXS Inc.

Mass / g Carbon / % Sulfur / %
0.1754 13.10 0.023
0.1744 13.07 0.021
0.1754 13.10 0.023
0.1757 13.03 0.022
0.1754 13.07 0.023
0.1749 13.09 0.022
0.1766 13.02 0.021
0.1760 13.04 0.022
0.1743 13.06 0.023
0.1770 13.07 0.022
Mean 13.06 0.022
STD 0.03 <0.001

 

Table 3. Limestone. Source: Bruker AXS Inc.

Mass / g Carbon / % Sulfur / %
0.2012 11.72 0.209
0.1957 11.73 0.210
0.1992 11.71 0.210
0.2061 11.72 0.206
0.1982 11.73 0.210
0.1889 11.71 0.209
0.1953 11.69 0.209
0.2004 11.73 0.207
0.2011 11.72 0.205
0.1978 11.72 0.210
Mean 11.72 0.209
STD 0.01 0.002

 

Table 4. Lime 1. Source: Bruker AXS Inc.

Mass / g Carbon / % Sulfur / %
0.2001 0.426 0.244
0.2025 0.430 0.244
0.2012 0.434 0.248
0.2028 0.429 0.246
0.2018 0.429 0.245
0.2007 0.432 0.249
0.2019 0.428 0.248
0.2001 0.429 0.248
0.2013 0.429 0.250
0.2007 0.431 0.249
Mean 0.430 0.247
STD 0.002 0.002

 

Table 5. Lime 2. Source: Bruker AXS Inc.

Mass / g Carbon / % Sulfur / %
0.2038 0.579 0.025
0.2027 0.579 0.025
0.2006 0.579 0.025
0.2003 0.578 0.026
0.2013 0.575 0.025
0.2018 0.576 0.023
0.2021 0.570 0.023
0.2016 0.581 0.023
0.2007 0.569 0.023
0.2050 0.570 0.024
Mean 0.576 0.024
STD 0.004 0.001

 

Reliable Analysis of Sulfur and Carbon in Limestone, Dolomite and Lime

Image Credit: Bruker AXS Inc. 

Summary  

Combining HighSense™ detection systems with the G4 ICARUS Series 2’s precise electronic flow control offers outstanding, long-time stable analytical performance. 

The robust HF-furnace fitted with the industry-leading ZoneProtect™ and its novel automatic cleaner guarantees minimal cost of ownership and high availability with less maintenance. 

The straightforward sample preparation used for this method does not necessitate any expert knowledge. The analytical performance in combination with the rapid analysis speed and ease-of-use makes the G4 ICARUS Series 2 the optimal choice for the quality control of limestone, burnt lime, dolomite and related products.

Reliable Analysis of Sulfur and Carbon in Limestone, Dolomite and Lime

Image Credit: Bruker AXS Inc.

This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.

For more information on this source, please visit Bruker AXS Inc.

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