Hierarchical high-value utilization of limestone resources: strategy optimization and cost comparison analysis

China’s calcium carbonate industry faces a critical triple challenge—structural mismatch between high-end shortages and low-end overcapacity, resource inefficiency, and environmental pressures—which calls for a systematic strategy aligning raw material quality with production pathways. This study conducts a comparative technical and economic analysis across five product lines (GCC, PCC, NCC, FACH, and FACO), establishing a hierarchical utilization framework based on feedstock suitability, process optimization, and cost modeling using Monte Carlo simulations and sensitivity analysis. Results reveal that raw material composition is the primary determinant of product viability: high-purity limestone (CaO >53%, SiO₂<2%, MgO<1%) is essential for premium NCC and PCC, while lower-grade ores suffice for GCC; process parameters, particularly carbonation temperature (14–70 °C) for nano-scale products, critically influence quality. Cost simulations show wide differentiation, with GCC the lowest (206.63 CNY/t ±21.00) and NCC the highest (633.96 CNY/t ±78.73) due to energy intensity, yet NCC achieves the highest profit margin from a market premium of 1,500 CNY/t, while energy inputs account for 77–96% of cost variance, underscoring efficiency improvement as a priority. The proposed hierarchical strategy—matching limestone grades to value chains—offers a clear pathway to enhanced resource utilization, and complementary roles for international best practices (e.g., CO 2 mineralization, automated sorting) and policy instruments (carbon taxes, CCUS subsidies) are assessed as enablers for sustainable transformation, collectively providing an evidence-based roadmap for reconciling economic competitiveness with environmental stewardship in China's calcium carbonate industry.

The global calcium carbonate market was valued at approximately USD 47.2 billion in 2021 and is projected to expand steadily at a compound annual growth rate of 4.88% during the 2022–2030 forecast period, with the market size expected to surpass USD 72.5 billion by 2030 (Precedence Research, 2022). Other study showed that the global calcium carbonate market size was estimated at USD 37.1 billion in 2025 and is projected to reach USD 70.1 billion by 2033, growing at a CAGR of 8.3% from 2026 to 2033 (Research and Markets, 2026). This forecast indicates that sustained demand from downstream application sectors, such as plastics, papermaking, coatings, and construction materials, will serve as the primary driver of the market’s robust long-term growth

China is the world’s largest producer and consumer of limestone (composed primarily of calcium carbonate), accounting for 70% to 75% of global demand (Research and Markets, 2025). By the end of 2022, the production capacity of China’s calcium carbonate industry stood at 70 million tonnes per annum (t/a), comprising 57 million t/a of ground calcium carbonate (GCC), 11.5 million t/a of precipitated calcium carbonate (PCC), and 1.5 million t/a of nano-calcium carbonate. Between 2016 and 2022, the production volume of ground calcium carbonate rose from 20 million tonnes to 57 million tonnes, representing a compound annual growth rate of approximately 19% (Guo et al., 2024), with with Henan Province possessing significant limestone reserves.

However, the development of the nano-calcium carbonate industry currently faces significant technical and industrialization bottlenecks. On one hand, high-performance nano-calcium carbonate demands strict control over key parameters such as particle size, crystal form, morphology, and surface modification; consequently, large-scale production encounters challenges regarding product performance stability, process controllability, and manufacturing costs. On the other hand, the large-scale production and economic viability of high-purity, high-performance nano-calcium carbonate remain critical factors constraining its further industrial application (Cai et al., 2026; Qiu et al., 2024; Boyjoo et al., 2014). This industrial pattern of “high-end shortage and low-end oversupply” severely restricts the sustainable development of China’s calcium carbonate industry.

In the resource development and utilization process, extensive production models have brought significant environmental and economic costs. Research indicates that when the MgO content in raw materials exceeds standards, low-melting-point calcium silicate compounds are generated during calcination, leading to kiln clinker formation and increased equipment maintenance costs (Ruan and Unluer, 2016; Li et al., 2014). Meanwhile, traditional calcium carbonate production has a carbon emission intensity as high as 1.8 tons CO 2 per ton of product. Based on China’s annual production of 40 million tons, the annual carbon emissions reach 72 million tons, accounting for 12% of the chemical industry’s total emissions (Li et al., 2025; Hanein et al., 2021). With the implementation of the EU Carbon Border Adjustment Mechanism (CBAM) (Wang et al., 2025), this high-carbon production model will increase export product costs by 23%, further weakening the international competitiveness of Chinese products Additionally, excessive development of low-end products causes rapid depletion of high-quality limestone resources, which is detrimental to the long-term healthy development of the industry (Yang et al., 2025; Lim et al., 2022).

From a technical perspective, important gaps remain in research on the compatibility between limestone raw material composition and production processes. Existing studies show that increased MgO content leads to lower formation temperatures of calcium silicate, directly shortening kiln service life (Ren et al., 2026). In nano calcium carbonate production, when SiO 2 content exceeds standards, it selectively adsorbs on the (001) crystal face of calcium carbonate crystals, inhibiting cubic crystal formation and reducing product specific surface area (Ruiz-Agudo and Cölfen, 2024). For food-grade calcium carbonate products, the occurrence forms of heavy metals such as arsenic and lead in raw materials and their removal mechanisms remain unclear, with existing purification processes showing insufficient arsenic removal efficiency (Lalkrishna et al., 2025). These technical bottlenecks severely restrict the development and quality improvement of high-end calcium carbonate products.

International advanced experience provides important reference for high-value utilization of limestone resources in China. Japan has established a comprehensive limestone resource classification system, dividing raw materials into 5 grades based on CaCO 3 purity, with pharmaceutical-grade products (purity >99%) commanding a market premium of 300%. German Bavarian calcium carbonate manufacturers innovatively employ amine absorption-desorption systems to recover CO 2 generated during calcination, purifying it to 99.5% before reusing it in carbonation processes, achieving over 80% CO 2 recycling rate. The United States developed ceramic membrane separation technology (pore size 0.1 μm) that enables food-grade calcium hydroxide to reach 99.95% purity while significantly reducing energy consumption compared to traditional chemical purification processes. These technological innovations not only improve resource utilization efficiency but also significantly reduce production costs and environmental burden (Tao et al., 2026; Nuithitikul et al., 2025; Gulamussen et al., 2022).

As an important inorganic chemical raw material, calcium carbonate production technology has made significant progress in recent years. GCC is prepared through mechanical crushing and grinding of natural calcium carbonate minerals. It has low cost and simple processes, and is widely used in plastics, rubber, coatings, and other fields, with particle size distribution and surface properties directly affecting application effectiveness. PCC and nano calcium carbonate are prepared through chemical reactions, offering high product purity suitable for high-value-added fields such as pharmaceuticals, food, and advanced coatings (Jimoh et al., 2018; Ramakrishna et al., 2017; Mattila et al., 2014), but with higher production costs. Food-grade calcium hydroxide and calcium oxide, due to their high purity requirements, require strict control of impurities such as silicon and magnesium in raw materials to meet the demands of pharmaceutical and food industries.

The selection of production equipment and process optimization have critical impacts on the quality and cost of calcium carbonate products. Jaw crushers and Raymond mills are core equipment for GCC production, but micronized powder yield is relatively low, requiring jet classifiers or vertical mill technology to produce ultrafine products. PCC and nano calcium carbonate production rely on lime kilns, digestion tanks, and carbonation towers, with process parameters such as calcination temperature (900 °C–1,200 °C) and carbonation reaction concentration (1–3 mol/L) being crucial for product crystal form and particle size distribution (López-Periago et al., 2010). Activation treatment through surface modification significantly improves calcium carbonate dispersibility and application performance, widely used in high-end products.

Hierarchical resource utilization is an important strategy for achieving efficient utilization of mineral resources. Research shows that graded allocation according to raw material quality can improve resource utilization rate and economic benefits. High-calcium limestone is suitable for producing nano calcium carbonate and PCC, while lower-quality limestone can be used for GCC or building materials. CO 2 by-products from production processes can be reused through carbon capture technology, reducing environmental impact (Jembere et al., 2024; Batuecas et al., 2021). Internationally, Europe and Japan lead in nano calcium carbonate and green production processes, while China has advantages in industrial scale but still needs improvement in high-end product technology levels.

The current policy environment in China provides favorable conditions for high-value utilization of limestone resources. The advancement of the “dual carbon” strategic goal has prompted relevant departments to further strengthen the requirements for green development in the mining industry. According to industry standards such as the “Specification for Green Mine Construction in Non-metallic Minerals Industry” (DZ/T 0312-2018), the construction of green mines requires mining enterprises to meet the national standards for the corresponding mineral types in terms of the “three rates” indicators: mining recovery rate, beneficiation recovery rate, and comprehensive utilization rate (Ministry of Natural Resources, 2018). The new regulation “Food Additive Calcium Hydroxide” (GB 25572–2010) tightened the arsenic content limit to 2 ppm, forcing enterprises to upgrade purification processes. In terms of policy support, the technology for producing calcium carbonate using CO 2 mineralization has been included in the “National Catalogue of Advanced and Applicable Processes, Technologies and Equipment for Comprehensive Utilization of Industrial Resources (2025 Edition)” issued by the Ministry of Industry and Information Technology. Furthermore, the National Development and Reform Commission and other departments have also released the “Green Technology Promotion Catalogue (2024 Edition),” aiming to promote advanced green technologies, including resource recycling. CCUS-related technologies are expected to receive policy support from this catalogue. These policy measures create a favorable institutional environment and market opportunities for high-value development and utilization of limestone resources. Against this background, conducting research on hierarchical high-value utilization of limestone resources in China has important theoretical and practical significance.

Raw material requirements

The main component of limestone is calcium carbonate (CaCO 3). Therefore, limestone suitable for producing calcium carbonate products should have high calcium content. Generally speaking, limestone with calcium content above 50% is relatively ideal, as higher calcium content can provide more calcium oxide (CaO), thereby improving lime production yield and quality. In actual production, to ensure that limestone calcium content meets requirements, chemical analysis and sampling tests need to be conducted before production feeding to determine compliance. Limestone purity is also one of the key factors in selecting limestone suitable for lime production. High-purity limestone can provide more stable chemical reactions and higher conversion rates, while reducing adverse effects of impurities on lime quality. Usually, limestone purity can be determined by detecting impurity element content, with lower impurity content helping to improve limestone reaction effectiveness and yield. Generally speaking, the component requirements for limestone in producing calcium carbonate products are: CaO ≥50–55%; MgO <1%; SiO 2 < 2%. Among these, CaO content >54% represents good raw material, >53% represents superior raw material, <50% represents inferior raw material, and 48% is the bottom line - production cannot proceed if lower. Raw materials exceeding specifications produce poor-quality products with high processing costs.

When producing GCC, since only crushing, grinding, and separation processes are required without calcination procedures, there are no strict requirements for SiO 2 and MgO content in limestone raw materials for GCC production. However, when producing PCC and nano calcium carbonate products, relatively high-grade limestone raw materials are required. For example, when limestone calcium content >50%, silicon-magnesium content must be <1%; when calcium content >51%, silicon-magnesium content must be ≤1%; when calcium content >52%, silicon-magnesium content must be ≤1.5%; when calcium content >53%, silicon-magnesium content must be ≤2.0%. This is because during calcination, impurity minerals such as SiO 2 and MgO react with calcium oxide to form low-melting-point, viscous calcium silicate and magnesium calcium compounds. These compounds adhere to kiln inner walls and can also bind lime into large blocks or sinter into clinker, affecting airflow and heat transfer within the kiln, causing “under-burning” and “over-burning” phenomena, and even damaging kiln equipment. Typically, kilns for calcining limestone are valued at tens of millions. These compounds mixed into products cause product quality problems in subsequent processes.

The limestone raw materials used in this experimental production have compositions as shown in Table 1. The calcium content of each limestone group exceeds 53% and 54%, silicon content is within 2%, and magnesium content is also below 1%. Therefore, the limestone composition used in this production can meet production requirements.

Production equipment

Main equipment for GCC production includes jaw crushers (as shown in Figure 1), Raymond mills, and dry classifiers. Jaw crushers are widely used for coarse and medium crushing of GCC raw ores (e.g., calcite, limestone, chalk, marble) to prepare for subsequent secondary crushing. The crushing chamber consists of a fixed jaw plate and a movable one mounted on an eccentric shaft. Driven by the shaft, the movable plate reciprocates periodically relative to the fixed plate. When it approaches, materials between the plates are crushed by compression; when it recedes, crushed particles smaller than the discharge opening fall out by gravity, while fresh feed enters the chamber for the next cycle.

Raymond mills (as shown in Figure 2), also called suspension mills, have a vertical structure with key components such as plum blossom frames, rollers, grinding rings, and scrapers. Materials enter from the side feed hopper. Rollers suspended on the frame revolve around the vertical axis while rotating themselves; centrifugal force makes them swing outward and press against the rings, while scrapers lift materials into the gap for crushing by rolling and pressing. These mills typically produce below 400-mesh with low investment and energy consumption. However, the compression mechanism yields limited fine powder–in 400-mesh product, particles <10 μm account for only about 36%. To produce 800–1250-mesh ultrafine GCC, modifications or external classifiers are added. However, the capacity remains small due to the low fine-powder content.

Working together with dry production crushing and grinding equipment are dry classifiers. The particle size quality of heavy calcium carbonate powder is closely related to the selection and use of dry fine classifiers. The jet classifier (as shown in Figure 3) selected for this experiment utilizes the wall attachment effect of high-speed jets to simultaneously separate materials into different fineness grades. Under the entrainment of compressed air, particles enter the classifier through the feeding nozzle. The trajectory of flowing particles is determined by air resistance and particle inertia. When passing through the wall attachment surface, flow deviation is formed due to the wall attachment effect, achieving classification results. Jet classifiers can produce 110–5,000-mesh heavy calcium carbonate products with processing capacity of approximately 100–500 kg/h.

Main equipment for PCC includes lime kilns (as shown in Figure 4), digestion tanks, carbonation towers, centrifuges, and dryers. Appropriate kilns produce high-activity lime, beneficial for subsequent digestion and carbonation, and affect crystal form, nucleation, crystal growth, and particle size distribution. Mechanical shaft kilns use countercurrent calcination, typically burning coke or anthracite, and are divided into preheating, calcination, and cooling zones. The preheating zone, located in the upper part, uses rising hot gas from the calcination zone to dry and preheat the limestone-fuel charge. The calcination zone, in the middle, is the main area for fuel combustion and CaCO 3 decomposition. The cooling zone, in the lower part, uses cold air from blowers to cool the quicklime below 100 °C before discharge from the kiln bottom.

The lime digestion equipment in PCC production is the digestion tank, which is the main equipment for generating Ca(OH) 2. After digestion is completed, the carbonation process of lime milk production takes place in carbonation towers using intermittent bubbling carbonation technology (as shown in Figure 5). After lime milk is pumped into the carbonation tower, a certain liquid level is maintained. CO 2 is bubbled from the bottom of the carbonation tower for carbonation reaction, controlling reaction temperature, concentration, gas-liquid ratio, and other process parameters. After carbonation ends, the generated CaCO 3 slurry is centrifuged to remove most of the water from the slurry, then dried and screened through airflow screens to produce corresponding products.

Production processes and procedures

Ground calcium carbonate

The process for preparing GCC is shown in Figure 6. First, select limestone with raw material composition meeting requirements, then wash and crush. Jaw crushers generally coarsely crush ore to about 5–10 cm before directly entering mills for production, or secondary crushing can be performed. Different mills are used according to the different mesh sizes of GCC being produced: Raymond mills for producing 100–400-mesh GCC; ring roller mills for producing 400–1,250-mesh GCC; vertical mills for producing 800–2500-mesh GCC; ball mill + classifier systems for producing 2,500–6,000-mesh GCC. Processed powder products are stored in tanks and then packaged separately.

Ordinary precipitated calcium carbonate

The preparation of ordinary PCC (Figure 7) involves crushing limestone to 5–10 cm and feeding it with refined coal into kilns. Calcination at 900 °C–1,200 °C (decomposition starts at 850 °C, completes at 1,200 °C) for 5–8 days yields CaO and CO 2; the latter is purified for carbonation. CaO is transferred to digestion tanks, where 15 min of digestion produces lime milk slurry. The slurry is screened, aged in settling tanks for 48–96 h, and its concentration adjusted in foam towers. The adjusted milk is carbonated with pure CO 2 in carbonation towers under conditions: CO 2 temperature 50 °C–70 °C, milk concentration 1.5–3.0 mol/L, reaction temperature 30 °C–70 °C, with crystal form control agents added as needed. The resulting PCC slurry is centrifuged to a paste with 25% water, then dried to <0.3% moisture. Finally, it is pneumatically conveyed through airflow screens and dust collectors to product tanks, and then packed.

Nano calcium carbonate

The preparation process for nano calcium carbonate is shown in Figure 8. Its preparation process and reaction principles are generally similar to those of ordinary PCC, because nano-grade calcium carbonate products are special, higher requirements exist for lime milk slurry, digestion water, and carbonation CO 2 purity. During production, settling time needs to be extended with filtration treatment to remove impurities and obtain refined lime milk slurry, while purifying water quality and purifying CO 2 gas used for carbonation. The carbonation process also differs from ordinary PCC. The carbonation process conditions for producing nano calcium carbonate are: CO 2 temperature 25 °C, lime milk concentration controlled at 1–1.5 mol/L, carbonation reaction temperature controlled at 14 °C–25 °C, with different crystal form control agents added.

Food additive calcium hydroxide

The process flow for preparing food-grade calcium hydroxide is shown in Figure 9. Because it is a food-grade product, requirements for silicon, magnesium, and other contents in limestone raw materials are quite strict. Raw materials cannot contain excessive impurity minerals; as excessive impurity minerals can easily harm human health. Limestone needs to undergo component selection in advance. Selected high-quality limestone is loaded into lime kilns and calcined into high-purity calcium oxide, then undergoes conventional digestion reactions to prepare Ca(OH) 2 slurry, followed by dehydration and drying. After drying to water content <0.3%, airflow conveyance to airflow screens is used, followed by conveyance through airflow screens and dust collectors to product tanks, then spiral conveyance from product tanks to packaging machines for final product packaging. Because it is food-grade, high purity requirements exist for products and reactants in all processes, with CaO and Ca(OH) 2 slurry requiring filtration and purification treatment.

Food additive calcium oxide

The process flow for preparing food-grade calcium oxide is shown in Figure 10. Production of food-grade calcium oxide is generally similar to production of food-grade calcium hydroxide, with one less digestion process, and raw material composition requirements are basically the same. Limestone must have high calcium content while silicon, magnesium, and other contents should be as low as possible. Calcium oxide generated after calcination must undergo impurity removal and purification treatment and be ground using mills. After component testing confirms compliance, it becomes the final product.

Costs analysis and comparison

The main costs of producing the above products include raw material costs, fuel (mainly natural gas and coal) and electricity costs, and labor costs. However, due to differences in processes and components between different products, there are differences in their production costs. The production costs could be calculated by the Equations 1, 2. where C p r o d u c t represents the production costs of the given products; C m a t e r i a l, C e n e r g y and C l a b o r represents raw material costs, energy costs and labor costs respectively. To be specific, the energy cost consists of coal costs, natural gas costs and electricity costs. The raw material consumption, energy consumption and labor costs of the production process of different products are shown in Table 2.

It should be noted that heavy calcium carbonate is made directly by mechanically crushing and grinding limestone, without the need for calcination or chemical reaction, so no coal is needed, and natural gas is mainly used to dry wet-milled products (assuming a wet-milling process is employed). Electricity is used for crushing, grinding and grading. The heavy calcium carbonate process is simple, with a high degree of automation and relatively low labor costs. When producing ordinary light calcium carbonate, nano calcium carbonate, food-grade calcium hydroxide and food-grade calcium oxide, natural gas and coal are required for calcination, and natural gas is also required for drying, digestion and surface modification (the process varies for different products). Labor costs are mainly determined by the complexity of the process. For example, aseptic operation is required when producing food-grade calcium hydroxide, and labor costs are relatively high. The prices of raw material and various energy are shown in Table 3.

All cost parameters employed in this investigation, including product yield ranges, fuel consumption coefficients, electricity intensity, labor requirements, as well as raw material and energy unit prices, were systematically sourced from an extensive market survey conducted under the framework of the research project supporting this study. The survey encompassed the predominant limestone mining operations, calcium carbonate processing facilities, and energy suppliers within the Hebi city and its adjacent regions of Henan Province in China, supplemented by publicly available market price data. More specifically, the yield rates and consumption coefficients were derived from the collection, compilation, and statistical analysis of actual operational records from cooperating enterprises and comparable production facilities operating within the region. The raw material and energy pricing data, in turn, were established through regional market price investigations and subsequently cross-validated against official mineral product price monitoring bulletins issued by local government authorities, as well as publicly accessible industrial and commercial energy tariff schedules.

Monte carlo simulation analysis

In order to effectively quantify the impact of various uncertain factors in the production process on the final total cost, this study uses the Monte Carlo Simulation (MCS) method for modeling and analysis. The Monte Carlo method is a numerical calculation method based on probability statistics theory and random sampling, which is suitable for processing complex system models with multiple uncertain input variables (Curto et al., 2022; Chou, 2011; Coates and Kuhl, 2003).

The implementation of Monte Carlo simulation usually includes the following steps: Define the problem and model. Identify the problem to be solved, build a mathematical model, determine the input variables (including deterministic and uncertain variables) and the output target.

Determine the probability distribution of the input variables. Assign a probability distribution to each uncertain variable.

Generate random samples. Use a random number generator to generate random values that conform to the probability distribution of each uncertain variable.

Run the simulation. Substitute the random sample into the model and calculate the output results. Repeat this process several times to obtain a sufficient sample size to analyze the statistical characteristics of the results.

Analyze the results. Perform statistical analysis on the simulation results and calculate the mean, standard deviation, confidence interval, quantile or probability distribution of the output variables.

Verification and optimization. Check the rationality of the simulation results and adjust the model parameters or increase the number of simulations to improve the accuracy if necessary.

Cost contribution is an indicator that measures the impact of each cost factor (raw materials, energy, labor) on the total cost fluctuation. In the model, this indicator is used to analyze the ratio of the standard deviation of each cost factor to the total cost standard deviation. The calculation formula is as follows:

The chemical composition of limestone raw materials is a key factor in determining the quality of calcium carbonate products. Analysis shows that limestone with a CaO content of 53%–55% and SiO 2 and MgO contents below 2% is suitable for the production of high value-added products such as nano calcium carbonate and light calcium carbonate (PCC). High CaO content not only improves calcination efficiency, but also reduces the formation of low-melting impurities such as calcium silicate and calcium magnesium, which can easily lead to nodules on the inner wall of the lime kiln, reduce product quality and increase equipment maintenance costs. In contrast, limestone with a CaO content of 50%–53% and a slightly higher impurity content is more suitable for the production of heavy calcium carbonate (GCC) because its process does not require high-temperature calcination and has a higher tolerance to SiO 2 and MgO. The influence of trace elements (such as Fe and Al) on the whiteness and surface properties of the product cannot be ignored. Studies have shown that excessive Fe content may cause the product to have a yellowish color, affecting its application in coatings and papermaking. Therefore, raw material screening needs to be combined with X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma spectroscopy (ICP-OES) analysis to accurately determine the component distribution and provide a scientific basis for the production of different products.

The cost analysis results show that heavy calcium carbonate has the lowest production cost, which is 140–278 CNY/t. The cost of light calcium carbonate is 341–752 CNY/t, and the cost of nano calcium carbonate is the highest, which is 382–879 CNY/t. The costs of food-grade calcium hydroxide and calcium oxide are 374–825 CNY/t and 363–874 CNY/t, respectively. Although nano calcium carbonate has a higher cost, its application in the high-end market (such as medicine and advanced coatings) is relatively broad, so the selling price is relatively high, about 1,500 CNY/t, showing the highest profit potential. The profit margin of food-grade calcium oxide is relatively low, reflecting the fierce market competition. In the future, it is necessary to reduce costs through large-scale production or process improvements.

The Monte Carlo simulation results of the production costs of the five products are shown in Table 4 and Figure 11, while Figure 12 represents the Monte Carlo simulation of sub-costs of different products. From the perspective of average total cost, the average total cost of heavy calcium carbonate is the lowest, which is 206.63 CNY/t, while the average total costs of nano calcium carbonate, food additive calcium hydroxide and food additive calcium oxide are relatively close, which are 633.96 CNY/t, 589.42 CNY/t and 621.99 CNY/t respectively, and the average total cost of ordinary light calcium carbonate is 553.44 CNY/t. Due to the extremely high actual yield of heavy calcium carbonate, relatively less resource input in the production process, and no coal consumption, its cost is the lowest among the five products. However, products such as nano calcium carbonate have a higher average total cost due to the relative complexity of their production process, high requirements for raw material purity and low actual output. The standard deviation reflects the degree of fluctuation of the total cost. The standard deviation of heavy calcium carbonate is 20.99 CNY/t, which is much lower than the other four products, indicating that its cost is relatively stable. The standard deviations of ordinary light calcium carbonate, nano calcium carbonate, food additive calcium hydroxide and food additive calcium oxide are 72.58 CNY/t, 78.73 CNY/t, 71.80 CNY/t and 83.29 CNY/t respectively. The costs of these products fluctuate greatly, affected by factors such as fluctuations in raw material prices, unstable energy costs or changes in labor efficiency during the production process. However, the main reason is that the price of coal is much higher than that of natural gas and electricity. The production process of heavy calcium carbonate does not involve the use of coal, while the other four products all use coal.

The minimum and maximum values of the costs reflect the product costs situation under the extreme conditions of fluctuations of various cost factors. The 95% confidence interval defines the possible range of total cost values. Taking heavy calcium carbonate as an example, its minimum and maximum costs are 140.00 CNY/t and 278.33 CNY/t respectively; the lower limit of the 95% confidence interval of the cost is 166.23 CNY/t, and the upper limit is 247.37 CNY/t, which means that at a 95% confidence level, there is a 95% chance that the total cost of heavy calcium carbonate is within this range. For enterprises, when formulating budgets and cost control strategies, they can refer to this interval to avoid costs exceeding expectations.

Figure 13 shows the distribution of the total unit cost of five products. Taking heavy calcium carbonate as an example, the probability density is relatively high when the cost range is 200.70–211.99 CNY/t, indicating that the cost of heavy calcium carbonate is more likely to appear in this range. For ordinary light calcium carbonate, the probability density is higher when the cost range is 529.39–579.58 CNY/t. This helps companies predict the possibility of cost occurrence and make cost response measures in advance. There are differences in the probability density distribution of different products. The probability density distribution of heavy calcium carbonate is relatively concentrated and single-peaked, while the cost probability density of nano calcium carbonate, food additive calcium hydroxide and food additive calcium oxide are all bimodal. This further confirms the results of the previous standard deviation analysis, that is, the cost of heavy calcium carbonate is relatively stable, while the cost of products such as nano calcium carbonate fluctuates greatly. Enterprises can formulate different cost management strategies based on the cost distribution patterns of different products, and strengthen cost monitoring and risk warning for products with large cost fluctuations.

Figure 14 presents the contribution of the three costs of raw materials, energy and labor to the total cost of each product, that is, the degree of influence. In heavy calcium carbonate, the contribution of energy cost is the highest, reaching 77.60%, the contribution of labor cost is 47.47%, and the contribution of raw material cost is 41.77%. In ordinary light calcium carbonate, nano calcium carbonate, food additive calcium hydroxide and food additive calcium oxide, the contribution of energy cost is also high, 96.36%, 92.66%, 89.95% and 88.48% respectively. This shows that energy cost occupies a dominant position in the total cost of these products. When enterprises are carrying out cost control, they should focus on the management of energy costs, such as optimizing energy efficiency and finding more stable energy suppliers. There are differences in the contribution of each cost of different products. The raw material cost contribution of ordinary light calcium carbonate is the lowest, only 17.86%, while the raw material cost contribution of heavy calcium carbonate is relatively high. The main reason is also that unlike the other four products, heavy calcium carbonate does not use coal in production. In terms of labor cost contribution, heavy calcium carbonate and food additive calcium oxide are relatively high. This is because the production process of these two products requires high labor skills or more labor input due to the complexity of the process.

The cascade utilization of resources is a key strategy to achieve efficient utilization of limestone resources. According to the raw material composition, high-quality limestone is suitable for the production of nano calcium carbonate and light calcium carbonate; medium-quality limestone is suitable for quicklime, slaked lime and ordinary light calcium carbonate; limestone with a CaO content of 50% but large fluctuations in impurities is used for heavy calcium carbonate; low-quality limestone is used for building materials and road construction. The terminal selling price of high-quality limestone for the production of nano calcium carbonate can be as high as 2,100 CNY/t, while the cost of producing heavy calcium carbonate with low-quality limestone is only 130–460 CNY/t, meeting the low-cost market demand. International experience shows that precise raw material sorting and intelligent production can significantly increase the proportion of high-end products. For example, Europe has significantly reduced production costs by optimizing raw material distribution through XRF online analysis and automated sorting systems. The CO 2 by-product in the production process can be reused through carbon capture, utilization and storage (CCUS) technology for carbonization reactions or the preparation of sodium bicarbonate, increasing economic benefits and reducing emissions. In line with the global carbon neutrality goal, regions rich in limestone resources can explore the use of CO 2 to produce low-carbon building materials, such as calcium carbonate-based concrete, to further achieve resource recycling.

In addition, it should be noted that the production process of calcium carbonate will have certain environmental impacts, among which CO 2 emissions and energy consumption are the key factors of environmental impact. The calcination process of light and nano calcium carbonate produces a large amount of CO 2, while heavy calcium carbonate has significant environmental advantages because it does not require calcination. Thedeployment of CCUS technology can reuse CO 2 for carbonization reactions and reduce carbon emissions. Optimizing the calcination temperature (900 °C–1,000 °C) and using efficient lime kilns can reduce natural gas and coal consumption and reduce energy consumption. The aseptic operation and purification process of food-grade products increase water resource consumption. It is recommended to introduce a closed circulation water system to improve utilization. To achieve sustainable development, the following measures can be taken. First, intelligent production transformation. Introduce sensors and AI control systems to optimize process parameters in real time and improve product quality and energy efficiency. Second, carry out green energy substitution. Gradually replace coal and natural gas with renewable energy to reduce carbon footprint. Third, implement by-product recycling. For example, waste slag can be used for low-end building materials production, and CO 2 can be used for carbonization reactions or low-carbon building materials to build a closed-loop economy.

The efficient utilization of limestone resources is the core driving force for the development of the calcium carbonate industry. This study revealed the key influencing factors for the production of ground calcium carbonate (GCC), light calcium carbonate (PCC), nano calcium carbonate, food-grade calcium hydroxide and calcium oxide by analyzing raw material composition, process parameters and cost. High-quality limestone is suitable for the production of nano calcium carbonate and light calcium carbonate, with high conversion efficiency and uniform particle size distribution; medium-quality limestone (50%< CaO <54%) is suitable for quicklime and slaked lime; low-quality limestone is used for heavy calcium carbonate and building materials. Process optimization shows that precise control of carbonization temperature (14 °C–70 °C). Cost comparison analysis shows that nano calcium carbonate has the highest profit margin, but food-grade calcium oxide has a lower profit margin (24%). In the future, the introduction of intelligent equipment and green energy can further reduce energy consumption and carbon footprint, laying the foundation for the sustainable development of the industry. Through systematic analysis, this study provides theoretical and practical guidance for the high-value and efficient utilization of limestone resources, and helps the green transformation of the chemical industry.

The future development of the calcium carbonate industry needs to seek a balance between technological innovation, resource optimization and green production. The application of intelligent production technologies, such as AI control systems and online monitoring equipment, can optimize process parameters in real time, improve product quality and energy efficiency, and is expected to reduce energy consumption by at least 10%. The development of new crystal control agents and microfluidic technology will further improve the dispersibility and functionality of nano calcium carbonate, meeting the refined needs of medicine and advanced coatings. Breakthroughs in CCUS technology, such as low-cost CCUS and calcium carbonate-based building materials production, will achieve resource recycling and help achieve carbon neutrality goals. In addition, the gradual replacement of renewable energy (such as biomass and wind power) will reduce carbon footprint and support the transformation of green chemical industry. Regional resource cascade utilization strategies need to combine big data analysis and precise sorting technology to optimize raw material distribution and increase the proportion of high-end products. Interdisciplinary cooperation, such as the integration of nanotechnology and environmental engineering, will promote the development of new calcium carbonate products and expand their applications in biomedicine and energy storage. Future research should focus on low-cost green processes, intelligent production and comprehensive utilization of by-products, build a sustainable calcium carbonate industry ecosystem, and provide a replicable green development model for the global chemical industry.