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Alternative Raw Materials

Substituting limestone with alternative calcium containing raw materials that are already decarbonated is an attractive option for reducing CO2 emissions. Such substition offers a dual advantage as not only the emissions linked to decarbonation of raw materials, but those linked to the fuel consumed for such dercarbonation can be eliminated.  Blast furnace slag, lignite ash, coal ash, concrete crusher sand, aerated concrete meal, corresponding fractions from demolishing wastes or lime residues from sugar industry are examples for such decarbonated alternative raw materials. However, the extent to which such alternatives can be used is governed primarily by:

  • composition of the conventional raw materials at the considered plant;
  • local availability and cost of decarbonated raw materials; 
  • their composition and particularly their silica, alumina, magnesia, sulphur, VOC or trace materials content;
  • possibilities to improve the qualities of raw materials by further processing.  

Alternative Raw MaterialsTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Use of EAF slag - CemStar®

As the calcination energy demand is estimated to be 1.9 GJ/t-clinker, substituting 10% of clinker with steel slag will reduce energy consumption by 0.19 GJ/t-clinker. 

Replacing 10% of clinker by steel slag can reduce CO2 emissions by approximately 11%

Equipment costs are mainly for material handling and vary between US $200,000 and $500,000 per installation. Total investments are approximately double the equipment costs. CemStar® charges a royalty fee.

Fly Ash as Raw MaterialCarbon content of the fly ash can help reduce fossil fuel usage (in the order of hundreds to thousands of kJ/kg-fly ash)

Japanese FlagCosts for a 2000 ton-silo and input facillities is reported to be between US $2.7 to 3.2 million [1US$=¥110].

Indian Flag For India, installation costs for a similar plant were reported to be $0.6 - 0.8 million. 

Calcareous Oil Shale as Alternative Raw Material

Energy consumption can be reduced by around 0.7 GJ/t portland cement. 

Some oil shale deposits may be partially decarbonated and their use would lead to reduced CO2 emissions from the calcination process. The amount of this reduction will depend on the extent that the oil shale is decarbonated and the amount of limestone replaced by the oil shale in the raw meal. 

Assuming that 8 percent of the raw meal is replaced with oil shale, an investment of US $1per annual ton of cement capacity would be required for installation of a feed system, and operating costs would increase by US $0.08/t cement (assuming that the source of the shale is close to the facility). 

Use of Slag as Raw Material

With slag use of 10 kg/t-clinker, energy consumption can be reduced by 17 kJ/t-clinker (APP, 2009). Substituting 15% of conventional raw materials by granulated steel slag is estimated to reduce thermal energy consumption by 0.1 to 0.4 GJ/t-clinker, and increase electricity consumption between 0 to 2 kWh/t-clinker (CSI/ECRA, 2009).

CO2 reduction are estimated at between 0 to 117 kg CO2/t-clinker (CSI/ECRA, 2009)

Investment and operational costs are estimated to be between € 0 to 6 million, and € 0 to 4.2/t-clinker, respectively (CSI/RECRA, 2009)

Carbide Slag as Raw Material

Not available

In a Chinese project, 184 thousand tons of CO2 reduction was forseen with the use of 315 thousand t/y of carbide slag and thereby substituting 432 thousand t/y of limestone. 

Total investments for utilizing 315 thousand t/y carbide slag was approximatly RMB 29.4 million (US $4.3 million [with 1RMB=US $0.146])