Natural stone sludge as secondary raw materials: towards a new sustainable recovery process

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Stone roofing in the Aosta Valley, Italy: Technical properties and durability of traditional Lithotypes

The Aosta Valley Region has promulgated in 1990 a law to partially finance stone roofs to the owners of houses in the historic centers of the valley, provided that the stone material chosen was suitable for this use. This suitability was certified by physical, mechanical and durability tests. More than twenty years ago, roofing slabs were extracted in north-western Alps mainly from schistose rocks. In recent time instead roofing slabs, according to global market, have an international origin. All the traditional stones tested showed excellent technical features according to the local legislation on roof slates. One of these traditional stones is a phyllite whose trade name is “Porfiroide” having the best physical and mechanical properties compared to the other kinds of traditional stones, but with a high standard deviation in the results of flexural strength performed after the freeze and thaw cycles. In the roofing installed 40 years ago, despite their best technical features, the “Porfiroide” roof slabs show a poor state of conservation with widespread detachments, fractures, growth of mosses and lichens, variations in colours. Otherwise, stones with a lower value of flexural strength and higher water absorption instead show good behaviour in the roofing in situ and also in terms of colour change. Evidently the only characterisation of the stone materials is not sufficient but it must be associated to a on-site verification, comparing each slab to be installed with a reference sample, part of the sample submitted to the tests, and to a control on site of the resistance of the stones to degradation

STONES SAWING SLUDGE AS BY-PRODUCT: characterization for a future recovery

The European Commission, as part of its Thematic Strategy on the prevention and recycling of waste, committed itself to tackle one of the issues around the waste definition, namely the distinction between waste and by-products. This definition has been outlined through the Communication on waste and by-product of the European Court of Justice (Brussels, 21.2.2007 COM(2007) 59 final COMMUNICATION FROM THE COMMISSION TO THE COUNCIL AND THE EUROPEAN PARLIAMENT). By-product is a substance or object, resulting from a production process, the primary aim of which is not the production of that item. By-products can come from a wide range of business sectors, and can have very different environmental impacts. If there is a possibility that the material is in fact not useable, because it does not meet the technical specifications that would be required for its use, then it should continue to be considered as a waste. The status of waste protects the environment from the potential consequences of this uncertainty. If it subsequently happens that a use is found for the waste in question then it will lose its status of waste and it will be considered a by-product. An incorrect classification could be the cause of environmental damage or unnecessary costs for business. For this purpose a characterization of sludge coming from different plants of stone processing was carried out for a better classification of the materials in view of a future recovery. The different stones cutting processes considered for this study are: gangsaw, diamond blade and diamond wire. The cut materials are granites, gneisses, and other stones mainly of silicatic nature. The tests performed on the sawing sludge are the following: particle size analysis, chemical analysis, wet magnetic separation, diffraction and SEM analysis. The study performed is useful for evaluating the possible reuses of the products coming from the magnetic separation: the metal fraction, and the mineral one. In order to avoid a subsequent environmental degradation and to promote a technology innovation (sustainability and circular economy) a proactive waste management strategy trying to optimize on the one hand the processing to obtain reduced waste and the other to improve the process to obtain two reusable by-products was considered

Ornamental stone cutting processing and sludge production evaluation with the goal of ending waste.

The End-of-waste concept was introduced by the ‘Thematic Strategy on the prevention and recycling of waste’ adopted by the European Commission, in which it proposed to specify the conditions for the cessation of waste status as part of the revision of the Waste Framework Directive (Directive 2008/98/EC). The Directive states that a waste shall lose its status if it is submitted to a recovery operation (including recycling) and comply with specific eligibility criteria. The strategic goal of the End-of-waste is to promote recycling, helping to ensure a high level of environmental protection through the reduction of the consumption of critical raw materials and the quantities of waste destined for disposal. In the mining sector, the reduction of landfill material may be obtained not only by finding a suitable recovery of the material as a by-product, but also identifying the best available cutting technique to be used on the basis of the physical, chemical and mechanical characteristics of the stones. The choice of the best cutting technique could lead to high efficiency and performance, high quality of the cut surfaces and a very low environmental impact by reducing energy consumption, decreasing the concentration of heavy metals in the sludge and producing less waste. In this context, an analysis of the procedures for cutting different types of ornamental stones into slabs together with the evaluation of sludge production for the different cutting methods has been carried out. Three types of analysis were conducted in parallel. The first concerns the characterization of the stones and the choice of the type of cutting machine. The analyses carried out were: petrographic analysis, compression strength, flexural strength, apparent density and water absorption. Also ultrasonic pulse velocity (UPV) and Knoop analyses were performed in order to establish the workability class of the stones, and their classification in accordance with previous research works (EASE R3). The second analysis involves calculating the amount of sludge produced in the three different cutting technologies, taking into account the same block characteristics. The third analysis was conducted on the sludge resulting from the processing of blocks cut into slabs. A comparison was carried out on the quality of the sludge produced, or type and quantity of metals present, taking into account the three different technologies. The tests carried out were: chemical analysis, magnetic separation test and SEM analysis of the metal fraction. The study could provide stone producers with a technological, scientific instrument to identify the best cutting techniques for the processing of their stones, in order to obtain a good efficiency process, optimize the recovery process, increase the economic advantages, and evaluate the possible reuse of the sludge through a proactive waste management strategy

Ornamental Stone Cutting Processing and Sludge Production Evaluation with the Goal of Ending Waste

In the quarry sector, the reduction of landfill material may be obtained not only by finding a suitable recovery of the material as a by-product, but also by identifying the best available cutting technique to be used on the basis of the physical, chemical, and mechanical characteristics of the stones. The choice of the best cutting technique could lead to high efficiency and performance, high quality of the cut surfaces, and a very low environmental impact by reducing energy consumption, decreasing the concentration of heavy metals in the sludge, and producing less waste. In this context, an analysis of the procedures for cutting different types of ornamental stones into slabs together with the evaluation of sludge production for the different cutting methods has been carried out. Two types of analysis were carried out in parallel: evaluation of the stones workability and calculation of the amount of sludge produced in the three different cutting technologies and from the cutting of blocks. A comparison was carried out on the quality of the sludge produced, on type and quantity of metals present, taking into account the different cutting technologies. The performed tests were: chemical analysis, magnetic separation test, and SEM analysis of the metal fraction. The study could provide stone producers with a technological, scientific instrument to identify the best cutting techniques for the processing of their stones, in order to obtain a high-efficiency process, optimize the recovery process, increase the economic advantages, and evaluate the possible reuse of the sludge through a proactive waste management strategy

Characterization of sludge resulting from the extraction and processing of natural stones. focus on a Piedmont case

The problem of the management of sludge resulting from the extraction and processing of ornamental stones is currently one of the key issues for the European Union and for Italy. The European Community, through Directive 2006/21/EC (Management of waste from extractive industries – Mining waste), Directive 2008/98/EC (Waste Framework) and Directive 1999/31/EC (Landfill Waste), has provided guidelines for its member countries on how to handle wastes, in view of a future sustainable development of the sector, especially as far as critical raw material (CRM) is concerned. In this context, an analysis of the procedure applied to extract and cut two similar Piedmont silicatic stones into slabs and to manage their sludge has been carried out. The ornamental stones taken into consideration are Diorite of Traversella and Perosa Stone (Dioritic gneiss). The following procedures were conducted to characterise the stones: petrographic analysis, as well as compressive strength, flexural strength, impact resistance and water absorption tests. This characterization is important to help choose the best available technique to extract and process the stones. The methodologies adopted in two different plants, according to their processed stones, are discussed hereafter. In addition, UPV and Knoop analyses were performed in order to establish the workability class of the two stones, and the classification developed in previous research works was applied. Subsequently, an analysis was conducted on the sludge resulting from the extraction and processing of blocks used for the production of slabs. A chemical analysis, a particle size analysis, a magnetic separation test, to obtain two fractions (metallic and mineral), and an SEM analysis of the two separated fractions were performed on the two sludges. This characterization was useful to understand whether the produced sludge could be recovered as by-products. The study will help stone producers to identify the best techniques for the extraction and processing of their stones, while obtaining less waste and less pollution

Marble Durability Assessment by Means of Total Optical Porosity and Adjacent Grain Analysis

The presence of pores, cracks and microcracks in marble is one of the main features that govern the processes of decay of this stone material and, although marble is characterised by a modest porosity, there is a clear correlation between the presence and movement of fluids, and the phenomena of alteration. Through the study of porosity, it is possible to better understand the phenomena of alteration and degradation in order to obtain useful information, not only in the field of modern building, but also for the protection and recovery of historical and artistic heritage goods. This study was conducted through the characterisation of parameters directly related with the degree of alteration of the materials: water absorption at atmospheric pressure (EN 13755), open porosity (EN 1936), flexural strength (EN 12372) and bowing (EN 16306 par. 8.2). The physical and mechanical measurements have been compared with the Total Optical Porosity method (TOP) and the Adjacent Grain Analysis (AGA) index (a suggested method to evaluate the marbles’ tendency to bow, in EN 16306 annex C); two different methodologies both based on image analysis. The purpose of this study is to demonstrate the effectiveness, for the assessment of marble durability, of the two techniques of microscopic image analysis, the first correlating to the grain shape and the second to the open porosity index. This was done by comparing the microscopic image analysis results with the physical and mechanical properties, both after artificial ageing and after ten years of natural ageing. The results obtained with the TOP method seem to represent the tendency to decay better than the AGA index. The comparison of image analysis of the thin sections, in different portions of the marble specimens, shows the development of degradation due to atmospheric agents, from the surface to the inside, of naturally aged specimens, confirming recent studies made on different marbles

CIRCULAR ECONOMY IN THE EXTRACTIVE SECTOR

The mining and the quarry sector shares the need to enhance the by-products as one of the most effective tools to limit waste production. This has the aim of minimizing the environmental cost of raw materials upstream production chains and to support research and technological innovation, providing opportunities for growth, competitiveness and creation of added value for important sectors. The exploitation of mines, quarries and the related treatment plants produces large quantities of "tailings". The by-product can be reused for different purposes within the construction supply chain (construction of road embankments, concrete, pre-mixed products, fillers etc.) thanks to their shape, size, physical and petrographic characteristics. For this reason it is essential to enhance the use of by-products of the extractive industry according to the last European regulation and implementing the National ones. In particular, the main crucial points in extractive industry to be faced and improved applying the Circular Economy approach are: - mining/quarry tailings. - sawing sludge from ornamental stone industry. - waste water from aggregate processing. The “circular approach” in the extractive industry is possible considering by-products in zero-waste supply chains as valuable secondary raw materials since the very beginning of every operation planning. A change in this vision is needed to sustain, also by means of proper indicator, an even more efficient circular economy

Vinyl-Asbestos Floor Risk Exposure in Three Different Simulations

Vinyl floors are widely used in public areas for their low cost and easy cleaning. From 1960 to 1980, asbestos was often added to improve vinyl floor performances. The Italian Ministerial Decree (M.D.) 06/09/94 indicates asbestos vinyl tiles as non-friable materials and, therefore, few dangerous to human health. This work aims to check through three different experimental tests if asbestos floor tiles, after decades of use, maintain their characteristics of compactness and non-friability. The effect of a small stone fragment stuck in the sole of rubber shoes was reproduced by striking the vinyl floor with a crampon. A vinyl tile was broken into smaller pieces with the aid of pliers to simulate what normally happens when workers replace the floors or sample it to verify the presence of asbestos. The third test reproduced the abrasion of the tile surface due to the dragging of furniture or heavy materials or sand grains that remain attached to the soles of shoes. The tests were carried out in safe conditions, working under an extractor hood with a glove box. Airborne sampling in the hood obtained the concentration of asbestos fibers produced in each test. The simulation tests performed confirms the possible release of fibers if the vinyl tiles are cut, abraded or perforated, as indicated by the Italian M.D

A new scientific approach to determine the stone workability

The prediction of stone ‐ diamond wire interaction is important for the extractive sector,  both  to  improve  the  productivity  and  efficiency  of  quarry  work  and  to  avoid  dangerous  and expensive endeavours of cutting when an unknown stone has to be introduced in the  plant. Combining  two simple  test as  the measurement of ultrasonic pulse velocity of  the  stone  and  the  Knoop micro  hardness,  a  scientific  classification  of  workability  have  been  found.  In  particular,  in  this  work  the  application  of  this  scientific  classification  methodology  to  the  stone  plant  has  been  studied,  performing  UPV  measurements  on  stone  block  before  their  cutting  The  correlation  of  ultrasonic measurements  by  indirect  method  with  the  index  HK25  allowed  to  order  the  stones  in  classes  of  workability  that  correspond  to what  the  owners  of  the  plant  used  to give  to  such  stones. Moreover  the  correspondence  with  the  in  situ  cutting  parameters  has  confirmed  the  reliability  of  this  scientific methodology.