Dr. Hakan Arden Kahraman – Technical Director – DMT Türkiye
Prof. Dr. Hakan Benzer – Hacettepe University Mining Engineering Department
Introduction
In a previous article, the general framework of geology and mineralogy for the concept of “geo-cementing” was established (Kahraman & Benzer 2024). This current paper aims to provide detailed information on the “geo-cementing” concept, emphasizing that the geology and mineralogy of the raw materials used in cement production directly impact the chemical composition, which in turn influences the quality of the cement produced. While the traditional approach to cement production has mainly relied on chemical principles to understand and control the properties of the final product, employing a mineralogical approach could yield more benefits. This approach can be linked to the original limestone depositional conditions and can facilitate better resource management by establishing a strong geological model that incorporates existing geological and mineralogical conditions to control the quality of the final product.
In the current political environment surrounding the industry globally, the cement industry is facing increased scrutiny from regulators, investors, and financial institutions to improve its operations. Financial institutions play a key role in promoting the adoption of CRIRSCO standards in the mining industry by integrating Environmental, Social, and Governance (ESG) criteria into their decision-making processes (Kahraman, 2024). Companies that adhere to CRIRSCO-compliant reporting are increasingly preferred by banks, investors, and other financial entities due to the growing emphasis on sustainable and responsible investment. Similar to the CRIRSCO template accepted in 2024, the new version of the JORC Code, to be released in 2025, will officially include ESG headings (Kahraman, 2024).
The “geo-cementing” approach, proposed in this paper, is similar to geo-metallurgy developed for metalliferous mines. It integrates geological, mining, comminution, and environmental information to optimize resource extraction and processing. This approach aims to bridge the gap between geological knowledge of limestone deposits and processing practices for the final product. Integrating geocementing into cement-making could enhance predictability and control over the production process, leading to improved product quality, cost savings, and more sustainable operations.
Geo-Cementing Concept
The term “geo-cementing” is derived from “geo-metallurgy”, which is used in metalliferous mining to bring together geological, mining, metallurgical, and environmental data to optimize resource extraction and processing. This approach offers a comprehensive view for understanding the variability of ore bodies and how this variability impacts processing performance. Essentially, it bridges the gap between geological knowledge of ore deposits and metallurgical practices for extracting valuable metals from them.
Geo-cementing involves the comprehensive study and management of geological materials such as limestone and clay used in cement production. It includes characterising, extracting, and optimising these materials to enhance the efficiency, quality, and sustainability of the cement manufacturing process. This concept connects the geological materials to the cement industry, making it more relevant and relatable for industry professionals.
The term encompasses the entire process of analysing the geological characteristics of raw materials, developing 3D geological models, planning quarry operations, and optimising the processing steps to produce high-quality cement. Key aspects of geo-cementing include raw material characterisation, comminution and cement-making process selection, process optimisation, and predictive modelling.
Raw material characterisation involves conducting mineralogy (identifying specific minerals present in the deposit), texture (examining spatial distribution and relationships between different minerals), liberation (determining the degree to which valuable minerals are physically separated from gangue or waste material), and particle size distribution analysis (examining the size distribution of ore particles affecting processing efficien cy).
Comminution process selection involves choosing the appropriate methods for crushing, grinding, and concentration of the raw material, while also selecting the most suitable extraction techniques based on the raw material’s mineralogical characteristics.
Process optimisation includes improving energy efficiency by minimising energy consumption during processing and reducing the environmental impact by decreasing the environmental footprint of mining and raw material conversion to cement product operations. This ideally leads to economic viability by maximizing the profitability of mineral extraction.
Predictive modelling involves process simulation using computer models to predict the behaviour of raw materials during processing. Once an acceptable model is established, the optimisation process can identify optimal operating conditions for maximum efficiency and profitability.
Steps for Geo-Cementing
To establish the general framework of geo-cementing, a number of steps need to be taken. These are given below.
1. Geological Characterisation of Raw Material;
2. Model Creation;
3. Quarry Development;
4. Quality Optimisation and Process Efficiency;
5. Managing Environmental Impacts; and
6. Managing Resources and Reserves.
In cement manufacturing, the primary raw materials are mainly limestone, clay, and gypsum. The quality of these raw materials directly impacts the quality and consistency of the final product, as well as the efficiency of the production process. As the major component in cement making limestone, following is considered for limestone quarry development, extraction and subsequent process strategies.
1. Geological Characterisation: By applying geo-cementing principles, a detailed understanding of the geological characteristics of the designated quarry is achieved. This involves data collection, mapping the mineralogical and chemical composition of the raw materials, understanding their spatial distribution, and identifying zones of high or low quality within the deposit.
Field Mapping: Conducting detailed field mapping to document any observable lithological differences at the surface, such as variations in colour, texture, or bedding, as well as any structural features present. Even in massive deposits, subtle changes can often be detected and recorded.
Core Logging: When drilling, performing meticulous core logging to capture subtle variations in mineralogy, texture, and structure is important. This allows geologists to identify features that might not be visible at the surface but are critical for defining lithological domains. This also allows to identify the mineralogical changes contributing to the chemical changes. This data is obtained from core drilling samples taken from various locations within the quarry to analyse the CaCO3, MgO, SiO2, Al2O3, S, contents using techniques like X-ray fluorescence (XRF). This data provides insight into the distribution of high-purity limestone within the deposit. For example, if limestone has low CaCO3 content, it may require the addition of corrective materials like bauxite or iron ore to adjust the composition, which can increase production costs and complexity. While some MgO is acceptable in cement, high levels can lead to the formation of periclase, which causes expansion and cracking in the hardened cement. Data collection should also focus on clay zones for SiO2 and Al2O3 contents. This data is integrated into the geological model to identify clay-rich zones with optimal SiO2 and Al2O3 levels. In addition, the data collection should consider any sulphur contributing zones as sulphur, often present as gypsum (CaSO4) or pyrite (FeS2), is needed in controlled amounts for the formation of ettringite, which controls the setting time of cement. However, excess sulphur can cause issues like clinker ball formation in the kiln. Furthermore, alkali content (Na2O and K2O) in limestone and clay samples in the deposit needs checking since it can react with reactive silica in aggregates to form alkali-silica gel, leading to expansion and cracking in concrete structures. The spatial distribution is mapped to manage the input of alkalis into the kiln.
Geophysical Logging: Borehole drilling should be accompanied by borehole geophysics. These should at least include gamma ray, density, sonic, electrical resistivity and conductivity logs. Gamma tool detects variations in the natural radioactivity of the rock with higher readings often indicating the presence of clay-rich zones, while lower readings suggest purer limestone. Density and sonic logs probs measure the density and acoustic properties of the rock, respectively, helping to identify zones with different lithological properties (e.g., denser dolomite versus less dense calcite). Electrical resistivity and conductivity measurements can distinguish between different lithologies based on their ability to conduct electricity, which varies with mineral content and porosity.
Mineralogical and Petrographic Analysis: A number of analytical techniques can be considered to characterise the raw materials. These may include thin section analysis, XRD (X-Ray Diffraction), and Scanning Electron Microscopy (SEM). Thin sections from drill core samples can be prepared and analysed under a microscope to identify differences in mineral composition, grain size, and texture. This method is particularly useful for identifying subtle lithological variations that might not be evident in hand samples. Using XRD will aid in quantifying the mineralogical composition of different zones within the deposit. XRD can reveal variations in the proportion of calcite, dolomite, clay minerals, and other constituents, even when these differences are not visually apparent. SEM coupled with energy-dispersive X-ray spectroscopy (EDX) provides detailed images and chemical analysis at a microscopic level, helping to distinguish fine-grained minerals and textures.
Sampling: When sampling highly homogeneous limestone deposits, the core sampling interval can vary from 1.5 to 3 m and can even go up to 5 to 10 m, depending on the deposit’s characteristics. To capture the variability in material composition, the drilling pattern should cover all parts of the quarry. In deposits with more variability or where specific lithological boundaries are of interest, a shorter interval of 1 m may be necessary to capture detailed variability. Borehole core diameters for samples typically range between HQ (63.5 mm) to NQ (47.6 mm). The choice of diameter depends on the degree of heterogeneity, with larger cores (HQ) providing more material for analysis and being preferable in variable deposits. Each sample should weigh around 1 to 2 kilograms, depending on the density of the limestone, which is generally enough for chemical and mineralogical analysis. If CRIRSCO-compliant resource and reserve estimations are considered, then all QA-QC procedures required by the CRIRSCO Codes need to be employed to avoid unbiased reporting.
Chemical Analyses: High-resolution geochemical profiling for major and trace elements is used for systematic geochemical samples collected from cores. This method allows identifying subtle geochemical signatures that correspond to different lithologies. For example, variations in Mg, Fe, or trace elements like Sr or Mn can indicate changes in mineralogy (e.g., from calcite-rich to dolomite-rich zones). The other parameters investigated include “Loss on Ignition (LOI)”, which measures the amount of volatile matter (e.g., water, organic matter) that is lost when the sample is heated to provide information about the purity of the raw material. pH determines the acidity or alkalinity of the raw materials to check the reactivity of the materials and the overall process chemistry. Using portable XRF analysers can also provide rapid, in-situ geochemical analysis. This tool can be employed both in the field and on core samples to quickly map out chemical variations across the deposit despite its limitations in the resource estimation process following the CRIRSCO codes.
Physical Tests: These tests include moisture content, bulk density, specific surface area, and grindability index. Moisture content determination provides information on the amount of water in the raw materials and helps control the moisture content during the clinkering process. Bulk density measures the mass of a unit volume of the raw material to calculate material quantities and optimize storage and transportation. The particle size distribution test determines the distribution of particle sizes in the raw materials. It helps to understand the grindability of the materials and optimize the milling process. The specific surface area test measures the total surface area of the particles per unit mass, which is essential for checking the reactivity of the raw materials during clinker formation. The grindability index test evaluates the ease with which a material can be ground to a specific particle size. It aids in selecting appropriate milling equipment and optimising energy consumption.
2. Model Creation by Using Geo-Cementing: Developing geo-cementing integrates geological, mineralogical, and processing data. The model should map the variability within the quarry, highlighting areas of different material quality by identifying the possible domains.
Domaining is the process of subdividing a geological model into distinct zones or domains based on specific geological, mineralogical, or geochemical criteria. Each domain represents a region within the deposit with relatively homogeneous properties, such as similar mineral composition, chemical characteristics, or physical attributes. Several parameters can be used to establish domains within a cement raw material deposit:
Mineralogical Composition: Domains can be established based on the concentration and distribution of primary minerals like calcite, dolomite, and clay minerals (kaolinite, illite, montmorillonite). For instance, a domain might represent an area rich in calcite, which is ideal for cement production, while another domain might represent a dolomite-rich zone requiring careful management. The presence of secondary minerals and impurities such as pyrite (FeS2) or gypsum (CaSO4) that contribute sulphur or other undesirable elements can define domains that need to be treated differently during extraction or processing. Domains can be designated similar to the ones given below:
• Calcite-Rich Domains: Identify zones where calcite (CaCO3) is the dominant mineral. These domains with high CaO and low MgO content are ideal for producing high-quality clinker with strong early strength. They require minimal corrective materials, making them ideal for clinker formation. However, the exact CaO yield will depend on the calcite purity and the presence of other associated minerals like quartz (SiO2) or clays. The presence of trace elements (e.g., Sr, Mn) should also be monitored as they can affect clinker properties.
• Dolomite-Rich Domains: Establish domains where dolomite (CaMg(CO3)2) is prevalent with elevated MgO levels alongside CaO. The MgO content must be carefully monitored to avoid the formation of periclase (MgO) in clinker, which can cause delayed expansion. These areas might pose challenges due to the introduction of MgO, which can affect clinker quality. Still, they might be strategically blended with calcite-rich materials to maintain an optimal chemical balance.
• Clay-Rich Domains: Map out areas with significant clay mineral content (e.g., kaolinite, illite). With high SiO2, Al2O3, and Fe2O3 content. The specific ratios depend on the clay mineralogy (e.g., kaolinite-rich clays offer a balanced SiO2/Al2O3 ratio). These domains are crucial for providing the necessary silica and alumina for clinker formation. However, careful management is needed to ensure that impurities (e.g., Na2O, K2O from illite) are controlled.
• Impurity-Rich Domains: Domains with higher concentrations of undesirable minerals (e.g., pyrite, gypsum, alkali-bearing minerals) may also be present in the deposit. These should be managed carefully to minimise their impact on cement quality.
Chemical Composition: Domains can be defined based on the concentration of CaO, derived from calcite. Areas with high CaO content may be prioritised for extraction to ensure a consistent feed for clinker production. MgO is a critical factor as high levels can negatively impact cement quality. Domains with elevated MgO concentrations can be identified and managed accordingly. Silica (SiO2) and alumina (Al2O3) are essential for clinker formation. Domains with optimal SiO2 and Al2O3 levels can be identified to produce clinker with desired properties, while areas with excessive or deficient levels can be managed differently. High alkali Content (Na2O, K2O) can cause problems like alkali-silica reaction (ASR) in concrete. Domains with high alkali content might be isolated or blended with lower-alkali materials.
Physical Properties: Domains based on the hardness of the material (e.g., soft calcite-rich zones vs. hard dolomite-rich zones) can influence grinding energy requirements and equipment wear. Domains based on porosity and moisture content affect the material’s handling properties and processing behaviour, such as drying or grinding efficiency.
Geological Structure and Continuity: Domains can also be defined based on structural features that affect the continuity and accessibility of the material. Fault zones, for example, might represent domains that require different extraction methods or pose a higher risk of material variability.
3. Application of Geo-Cementing in Extraction Strategies: Geo-cementing can significantly enhance the development of extraction strategies, optimising resource usage in several ways. Based on the geo-cementing model, the extraction of raw materials can be planned to optimise the quality and consistency of the feedstock. This may involve selectively mining certain areas or blending materials from different zones to achieve the desired chemical composition. For example, calcite-rich domains can be targeted for consistent high-CaO feedstock. Similarly, domains with different properties can be blended at the extraction stage to achieve a balanced raw mix. For instance, high-CaO domains can be blended with high-SiO2 domains to meet the desired chemical composition for clinker formation. By extracting from domains that require less corrective material, energy, or processing adjustments, operational costs can be minimised. For example, avoiding high-MgO domains can reduce the need for costly adjustments in the kiln operation. Domaining also helps in identifying areas with excessive impurities or undesirable minerals that might otherwise lead to higher waste production. These areas can be avoided or managed with specific processing techniques. Using real-time data from the geological model to blend materials at the extraction stage reduces the need for later adjustments in the raw mix and ensures a more consistent feed to the kiln. In addition, updating the 3D geological model with ongoing data to refine domains and adjust extraction plans to respond to any unexpected variability in the material dynamically. For example, if a certain area of the quarry produces materials that lead to suboptimal clinker formation, the plan can be adjusted to target more suitable areas. Additionally, in terms of environmental and sustainability considerations, domaining and geo-cementing allow for better long-term planning, ensuring that high-quality material is used efficiently, and low-quality material is either improved through blending or left as future resources. Emission zones and subsequent extraction strategies can also be established and better controlled during processing by understanding the spatial distribution of sulphur-bearing minerals or high-alkali zones. This will lead to the simulation of various scenarios, such as how different blends of materials will affect processing efficiency or final product quality. This helps in planning the extraction and blending strategies.
4. Quality Optimisation and Process Efficiency: The cement production process involves several energy-intensive steps, including raw material grinding, heating in the kiln, and clinker grinding. Geo-cementing allows for predicting how different materials will behave during processing. For instance, certain minerals might require higher kiln temperatures to form clinker or might influence the grindability of the material. Knowing this in advance allows for optimising the kiln and grinding processes ensuring energy is used efficiently and clinker quality is optimised. The efficiency of these processes can be significantly influenced by the mineralogy and chemistry of the raw materials. Applying statistical methods like cluster analysis to categorise different lithologies based on the combined dataset can be particularly effective when dealing with massive deposits where traditional visual classification is challenging. Adopting machine learning models using the collected data to predict lithological variations in areas with sparse data can refine the geological model and improve the accuracy of lithological domains. Implementing in-situ monitoring techniques, such as near-infrared (NIR) spectroscopy, during drilling or blasting to provide immediate feedback on lithological variations ensures that adjustments can be made in real-time. With a deep understanding of the raw material properties, kiln operations can be fine-tuned. For example, knowing the exact mineralogical composition allows operators to optimise the temperature profile within the kiln by using sensors to monitor temperatures and adjust them based on the mineralogy of the feed. This ensures optimal clinker formation and energy efficiency, which can improve the formation of clinker phases, reduce energy consumption, and lower CO2 emissions. Similarly, the grindability of the raw materials can vary based on their mineral composition. By understanding these variations, the grinding process can be optimized to achieve the desired fineness with minimal energy input. This not only reduces power consumption but also enhances the efficiency of subsequent steps like clinker formation and cement grinding. Furthermore, geo-cementing data can also be used to predict equipment wear and tear. For instance, harder or more abrasive materials may lead to increased wear on grinding equipment, necessitating more frequent maintenance or adjustments to the process. The data from processing can be fed back into the geo-cementing model to refine it further. This continuous feedback loop helps in adjusting quarry development plans and processing strategies, ensuring a dynamic optimisation process as well as implementing strict quality control measures to predict and control the quality of the final product. This ensures that the cement meets the required specifications consistently.
5. Managing Environmental Impacts: Cement production is a major contributor to greenhouse gas emissions and environmental degradation due to quarrying activities. Geo-cementing can play a crucial role in mitigating these impacts by optimising the use of raw materials to reduce the amount of waste generated during quarrying and processing. This includes reducing the volume of overburden, fines, and other by-products that may otherwise be discarded. Lower emissions can be another area by optimising the kiln and grinding processes based on a detailed understanding of the raw materials. This can lead to more efficient fuel use and lower CO2 emissions. Additionally, optimising the raw material blend can reduce the need for corrective additives, further minimizing emissions. Finally, geo-cementing data can also establish more sustainable quarry management practices by mapping out highquality reserves. Companies can plan their extraction activities to minimize the environmental impact, such as by reducing the footprint of active quarry areas or prioritising the use of lower-impact extraction methods.
6. Resource Management: Effective resource management is critical in the cement industry, particularly as reserves of high quality raw materials increasingly become scarcer. Geo-cementing provides tools and techniques for more accurate and efficient resource estimation and management. Geo-cementing models provide a detailed understanding of the quantity and quality of available resources. This allows for a more accurate estimation of the lifespan of a quarry, as well as better planning for future resource needs. In addition, with detailed information about the quality and spatial distribution of raw materials, cement producers can develop long-term strategic extraction plans that maximise the value of their resources. This might involve sequencing the extraction of different zones to ensure a steady supply of raw materials that meet production requirements. Therefore, as the cement industry increasingly adopts frameworks like the CRIRSCO templates for resource and reserve reporting, geo-cementing can support compliance with these standards. By providing robust, data-driven insights into the quality and quantity of raw materials, companies can produce more transparent and reliable reports, which are crucial for stakeholders, including investors and regulators. Banks, investors, and other financial entities increasingly favour companies that adhere to CRIRSCO-compliant reporting, as it aligns with the growing emphasis on sustainable and responsible investment.
Conclusion Incorporating geo-cementing into cement production offers significant advantages in terms of optimising raw material quality, improving process efficiency, reducing environmental impact, and enhancing resource management. These benefits align with broader industry trends towards sustainability, operational efficiency, and compliance with global reporting standards, making geo-cementing a valuable tool for modern cement producers.
The interplay between raw material quality optimisation and process efficiency within geo-cementing principles is crucial for optimising cement production. By developing these principles into quarry development and product quality strategies, cement producers can achieve more consistent product quality, enhanced process efficiency, reduced environmental impact, and better resource management. This approach not only aligns with modern industry standards but also provides a competitive edge in the market. In essence, geo-cementing plays a vital role in ensuring the sustainable and efficient extraction of mineral resources, meeting the growing demand for cement while minimizing environmental impacts. In summary, geo-cementing can provide the following benefits:
• Improved Efficiency: Geo-cementing insights lead to more efficient extraction and processing processes by guiding exploration efforts to discover high-grade areas;
• Reduced Costs: Optimised processes can lower production costs by optimising quarry design and cost-effective processing plant operations based on raw material characteristics by ensuring consistent product quality throughout the production process;
• Environmental Sustainability: Geo-cementing can help minimise the environmental impact of the quarrying and comminution process by minimising waste generation and maximising resource recovery.
• Resource Conservation: By understanding material characteristics, geo-cementing can help to maximise the recovery of the raw materials.
References:
Kahraman Arden H. & Benzer H. 2024. Geo-cementing: Influence of Raw Material Mineralogy and Geology on Cement Quality. CemenTürk. pp.50-56, Dec. Issue.
Kahraman Arden H. 2024. The Cement Industry’s Preparedness for Resource and Reserve Estimation: Implications for Mergers, Acquisitions, Financing, and the Paris Agreement. TurkCement Magazine. October Issue. pp.66-70.
