Using XRF to Determine Free Lime Content in Clinker for Cement Quality Control

High product quality with low energy consumption is the key objective of successful cement production these days. The free-lime concentration in the clinker produced in the kiln process is a key factor. When this value is between 1 and 1.5%, optimum energy consumption with maximum kiln reactivity is achieved. Thus close monitoring of the free-lime concentration is needed for optimum operating conditions. When the kiln is run under these conditions, significant fuel savings and a decrease in CO2 emissions can be achieved.

Free Lime in Cement

Excess free lime in cement leads to expansion effects. Hence it is critical to measure free-lime content. Conventional methods for free lime content determination are wet chemical methods such as titration, X-ray fluorescence (XRF), and X-ray diffraction (XRD) techniques, which have their own limitations. The S8 LION spectrometer with simultaneous wavelength dispersive X-ray fluorescence (WDXRF) provides a free- lime channel based on the XRD technique in cement plants where free-lime analysis is required for process control. The XRD free-lime channel determines the elemental composition and free-lime content rapidly and accurately using a single sample in one run.

This report demonstrates the analytical performance of the S8 LION in free-lime content determination for the monitoring and optimizing of the cement production.

Instrument

The S8 LION is designed for quality and process control in cement production, mining and the industrial minerals processing. It has the following advantages:

  • Industry grade system
  • Reliable operation and high instrument uptime
  • Short time-to-result
  • High accuracy
  • Enables immediate feedback and quick process adjustment

The S8 LION employs SampleCare technology with a sample loader and tube-above geometry and handles the pressed pellets with care and hence dust and debris from pellet breakage does not affect the instrument. The sample loader ensures optimum presentation of the sample. Accurate sample surface positioning, adjusted temperature control, the temperature-stabilized enclosure and the constant vacuum all enable high analytical precision even for the light elements.

The spectrometer enclosure of the S8 LION is sealed against dust to ensure maximum instrument uptime even under harsh conditions. The unique TouchControl interface allows the S8 LION to be operated in island mode without a PC. TouchControl also helps simple and failsafe starting of the samples leading to enhanced productivity.

The S8 LION can have up to 13 element channels and one free-lime channel (XRD) for all analytical tasks for raw mix, clinker and cement control. Each channel is optimized for specific elements and their concentration range.

Sample Preparation

Samples were prepared in the form of pressed pellets in 51.5 mm steel rings with the help of the automatic press and mill from Polysius. Two grinding-aid tablets were added for grinding to the clinker. The pellets were pressed under a weight of 5 tons.

Measurement

Measurements were carried out on the S8 LION with simultaneous WDXRF and a free-lime channel. The S8 LION, which rapidly quantifies free-lime content in clinker samples and helps in process control, has 10 channels for Na, Mg, Al, Si, P, S, K, Ca, Ti, Fe and the free lime channel (XRD). A 4KW Rh target X-ray tube was used. The integration time was 60 s for free lime.

Results

For calibration of the S8 LION for free-lime quantification, standard samples of 0 – 4% concentrations were used. The results were validated with TOPAS Rietveld analysis using a dataset from the D4 ENDEAVOR. Four different sample scans are shown in Figure 1.

Due to the use of Rh radiation, the scattered radiation and sample fluorescence is very low, leading to a reduced background. It is clear from the scans that the S8 LION is the apt tool for determining free lime in process samples from 0.1 % upwards.

The free-lime channel was calibrated based on four standard samples. The calibration curve is depicted in Figure 2. The calibration details are summarized in Table 1. The regression has a standard deviation of 0.14% and the resulting LLD for free lime is 90 ppm.

Standard Name Chemical Concentration [%] XRD Concentration [%] LLD (PPM)
FL-Std 1 Trace 0.15 90
FL-Std 2 0.83 0.69 90
FL-Std 3 3.29 3.22 90
FL-Std 4 4.00 4.07 90

One clinker sample was studied 10 times to verify the reproducibility of the free-lime channel. The summarized results are given in Table 2. The S8 LION achieves a 0.013% absolute standard deviation for one sample with 0.75% free-lime content.

Time Sample 1 Free-Lime (%) Sample 2 Free-Lime (%)
1 0.76 2.90
2 0.78 2.93
3 0.74 2.89
4 0.76 2.89
5 0.76 2.96
6 0.75 2.92
7 0.74 2.97
8 0.76 2.93
9 0.74 2.95
10 0.75 2.97
Average 0.75 2.93
Abs. Std. Dev. 0.013 0.03
Rel. Std. Dev. 1,73 1.05

Conclusions

The S8 LION with a free-lime channel offers precise and reproducible determination free-lime content in clinker and cement samples across the concentration range required for process control. The free lime data can help in monitoring and adjusting the kiln process and to achieve significant fuel savings.

Integrating elemental analysis using simultaneous XRF and the free-lime channel based on XRD technology in one device permits all basic parameters to be monitored under the same conditions using a single sample in one run. This decreases handling time and sample preparation and instrumentation time. The S8 LION is reliable and helps achieve maximum uptime and precision.

This information has been sourced, reviewed and adapted from materials provided by Bruker X-Ray Analysis.

For more information on this source, please visit Bruker X-Ray Analysis.

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Comments

  1. samir elhoseny samir elhoseny Egypt says:

    why mutiply 0.28 in calaculation of free lime in cement by HCL?

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