by Thomas Foschini14   Dicembre   2018

Super-white body is eco-friendlier with zirconium silicate

The results of the first LCA (life cycle assessment) study comparing alumina and zirconium silicate in ceramic body preparation have been published

The use of zirconium silicate in place of alumina in ceramic body formulations for super-white tiles (L>85 in the CIE Lab colour space) mitigates many of the environmental impacts of the production process. This conclusion emerged from the first comparative study based on LCA (life cycle assessment) methodology commissioned by the Zircon Industry Association (ZIA) and carried out by thinkstep Italia in collaboration with Centro Ceramico di Bologna and subject to review by a panel of independent international experts.
“The study was divided into two steps,” explains Andrea Morfino from thinkstep Italia. “The first step consisted of a life cycle analysis of zirconium silicate in the context of the mining industry. The second step focused on its use as a whitening agent in the ceramic industry and involved conducting a comparative analysis against the main competitor material, alumina (obtained from bauxite by way of a chemical refining process).”
The study obtained the data for alumina production from a previous LCA conducted by European Aluminium (EA). The entire study was conducted in compliance with international ISO standards. “As a further assurance of the reliability of the study, in the case of comparative analyses the standard requires evaluation by an independent commission made up of three leading experts in the field of LCA applied to the mining and ceramic industry.”
 

Before discussing the results, it is important to clearly understand the concept of LCA. In accordance with international standards ISO 14040 and ISO 14044, it is a methodology that provides an objective assessment of the potential environmental impact of a process “from cradle to grave” or, as in the case of application in the ceramic industry, “from cradle to factory gate”. The analysis takes account not just of the environmental costs of extracting and refining raw materials but also of the repercussions that the use of a given component may have on the mixture of materials making up the ceramic body and its consequent environmental impact assessment.
“In the life cycle analysis the comparison is meaningful exclusively within the context of the product or services analysed. For this reason, it is not just defined by a number but by variables that include quantity, quality and where necessary also time.” The various body formulations to be used in the study were chosen in collaboration with Centro Ceramico. “We took as our benchmark the production of a full-body porcelain tile with a level of lightness (L in the CIE Lab colour space) greater than 85, known as ‘super-white’,” explains Maria Chiara Bignozzi, director of Centro Ceramico. “The doses normally used were determined on the basis of interviews with companies and other indications and used to obtain 3 different formulations based on zircon sand and another 3 based on alumina,” she continued.
Various precautions were taken in this stage given that the actual formulations used by companies must take account above all of the degree of purity of the various raw materials. However, based on the cases considered (and taking account of a certain variability in the real conditions of use, notes Bignozzi), it was observed for example that the prevalent use of zirconium silicate in place of alumina leads to a reduction in the quantity of feldspars in the process due to the differences in behaviour between the two substances in the kiln determined by their different particle size distributions. “What is by no means obvious is how to establish objectively the repercussions that this can have in terms of the LCA, even if we consider only environmental performance at the application stage and not the stages of extraction and refining,” explains Andrea Morfino from thinkstep.
As for the main stages and results of the study itself, thinkstep collected primary data for global production of zirconium silicate (the examined data cover more than 77% of world production). For zirconium silicate, the main item of consumption in terms of the LCA during extraction is electricity, along with a small quantity of fossil fuel (natural gas) consumed during refining, which essentially consists of a mechanical separation process.
 

These data were included in the LCA model specially created using the GaBi life cycle engineering software and integrated with the data obtained from the body formulations established with the Centro Ceramico. The first output of the study was the environmental performance of 1 kg of zircon sand. “At this point we retrieved the LCA data for alumina and inserted them into the model, taking care to replicate the same conditions of use. This was an essential step in terms of the reliability of the comparison,” observed Andrea Morfino.
The comparative results for potential environmental impacts can be expressed in terms of the acronyms used in all life cycle assessments. The most important are: global warming potential (GWP), soil and water acidification potential (AP), eutrophication potential (EP), ozone depletion potential (ODP), photochemical ozone creation potential (POCP), primary energy demand (PED), water consumption (WC), abiotic depletion potential for elements (ADPe) and abiotic depletion potential for fossil fuel (ADPf).
“In all the formulations considered, we found the values for the potential environmental impact of zircon sand-based super-white bodies to be lower than those found for alumina-based formulations.” Specifically, ADPe (abiotic resources) was more than 50% lower, while the other indicators showed differences of between 20% and 22%.
The first and in percentage terms most significant reason for this concerns the stages of mining and refining. “Unlike zirconium silicate which can be mined and refined through a simple process of mechanical separation and elimination of impurities, alumina does not occur in nature in a form that is immediately available for use. It is obtained by mining the sedimentary rock bauxite and carrying out a refining and chemical purification process known as the Bayer process, which requires the input of significant quantities of resources such as complex fossil fuels, sodium hydroxide, calcium oxides, etc.”
This explains the more than proportional reduction in most of the environmental indicators. “Take for example water acidification or global warming. From an LCA perspective, these variables are influenced more by the process of mining and processing the raw material than by transport.” In other words, it is the emissions of the fossil fuels used in the refining process that make the biggest contribution to global warming and the by-products of the process that cause the so-called “acid rain” responsible for acidification of water and soil.
The second part of the study focused on the LCA of the mixture. The use of smaller quantities of feldspars in zirconium silicate-based formulations reduces the environmental impact of the process because feldspar itself is produced by means of a mechanical refining process that is generally more complex and has a bigger environmental impact (for example due to the consumption of lead and silver) than the process of quarrying clays, which are present in a more than proportional percentage in zirconium silicate-based super-white bodies.
 

The last but not least important aspect of the study concerns electrical energy. Although no significant differences between the different formulations are observed in terms of application (in other words, all the formulations give similar results in terms of their comparative environmental impact reduction), the result may be significantly affected by the different ways in which electrical energy is produced (such as fossil fuels, nuclear fission or renewables) in different countries, especially those where the mining and refining operations are performed.
Valid within Europe (geographical location must be considered because the study includes the environmental costs of raw materials transport and all other significant parameters such as the energy mix used for electricity production in individual countries for the purposes of the Impact Assessment IA), the complete LCA study will soon be available on the ZIA website, where key documents and summary results are already available for download. It represents the basis for further scientific publications by the parties involved (ZIA, thinkstep and Centro Ceramico) in international life cycle assessment magazines.
For the ceramic tile manufacturers this marks a further major step forward in the definition of an EPD (environmental product declaration) for ceramic surfaces.
 

th.foschini@gmail.com