Mineral product with a respirable silica content not posing health risk

Abstract

The subject of the invention relates to a health and environment friendly fine mineral product with quartz and feldspar contents, said product comprising a quantity of respirable silica that does not pose a health risk according to the standards and further possessing the technical properties similar to those of the fine quartz products comprising a quantity of respirable silica that poses a health risk according to the standards. The product according to the invention comprises 10-50% by weight ground feldspar and 50-90% by weight ground quartz so as to have a final respirable crystalline silica content of 0.3-1% by weight.

Description

[0001] DESCRIPTION

[0002] MINERAL PRODUCT WITH A RESPIRABLE SILICA CONTENT NOT POSING HEALTH RISK

[0003] Subject of the Invention

[0004] The subject of the invention relates to a health and environment friendly fine product with quartz and feldspar contents, said product comprising a quantity of respirable crystalline silica that does not pose a health risk according to the standards and further possessing the technical properties similar to those of the fine quartz products comprising a quantity of respirable silica that poses a health risk according to the standards.

[0005] State of the Art

[0006] Quartz, one of the most abundant minerals in nature, is used in high quantities as a glass former, backbone former, corrosive additive or filler in the manufacture of glass, ceramic sanitary ware, rubber, electronics, tiles, and paints, based on its purity and crystalline structure. Quartz, due to its silica (SiOz) content of 95-99% by weight, is a hard, crystalline mineral with a low thermal expansion coefficient and a high chemical resistance. However, in case the quartz, which comprises fine-sized silica particles according to the field of use, is inhaled, the silica particles may accumulate in the alveoli and may cause silicosis, a permanent occupational disease with the possibility of becoming fatal in cases of prolonged extensive exposure. The respirable crystalline silica (RCS) quantity is evaluated according to the standard EN 481. According to EN 481, the risk of reaching the alveoli is 4.6% for the free silica with a size below 5 microns, 42% for the free silica with a size below 2.7 microns, and 68.6% for the free silica with a size below 2.2 microns.

[0007] In the production of fine quartz, the vacuum or closed-circuit systems are used in order to prevent the inhalation of silica especially during the handling. It is known that the users in the fields where the fine quartz is used as a raw material, in case they have awareness, take measures to retain the dust, restrict the use of silica, carry on the processes by the use of dust masks and ventilation, and conduct studies to develop artificial substances with similar properties to those of quartz. However, it has not been possible to develop a substance, which has all the technical properties of fine quartz and which causes no adverse effect on the health of the living beings. Even if such a substance exists, the state of the art has not yet been able to discover it. Despite all its adverse effects, the quartz is used mandatorily in some fields. Due to the inhalation risk, the fine quartz may not be used or the use thereof is limited in the new fields with high potential of providing added value. Consequently, the manufacturers who process the quartz mineral and use high quantities of quartz as a raw material are in search of the substances, which possess the properties similar to the technical properties of quartz enabling this mineral to be preferred in such fields, allow a reduction in the quantity of quartz used, and lack any adverse health effect.

[0008] Our country is in a geography rich in the sodium feldspar mineral. The feldspar reserve of Turkey accounts for around 14% of the worldwide reserve. Feldspar is used in high quantities as a sintering agent in the ceramic and glass industries and as a filler or a functional additive in the rubber, plastic and paint industries. Despite having quite low respirable silica content, the feldspar has technical properties similar to those of the quartz with high respirable silica content. While the feldspar, owing to its alumina content, improves the hardness, durability and chemical corrosion resistance of the finished product, it also serves as a barrier by lowering the melting temperature of the finished product, owing to its calcium oxide, potassium oxide and sodium oxide contents. The hardness value of feldspar is very close to the hardness value of quartz. For these reasons, it is envisaged that it would be possible to obtain the products, which, although comprising a quantity of respirable silica not posing a health risk according to the standards, possess the properties similar to those of the products with high fine quartz content, by using a quantity of fine quartz, which is lower than the quantity of fine quartz in the conventional products, and a certain quantity of feldspar.

[0009] Within the scope of the invention, a fine product has been developed by mixing the fine quartz and the feldspar according to certain proportions, said fine product, although having a lower respirable silica content compared to the respirable silica content of the conventional quartz products used according to the state of the art and carrying no health risk according to the standards, still possessing the technical properties similar to those of said conventional quartz products. Whereas, due to the adverse health effects of the respirable silica content, the use of the quartz, which is purified and reduced to certain particle size, remains limited according to the state of the art or the quartzcomprising products may not be used in any way in the potential fields, e.g., in the polymer industry, it will be possible to comfortably use the ultra-fine purified product according to the invention in such fields. It will be possible to use the product according to the invention in the field of polymers where, the fine quartz, although being currently needed, may not be used in any way due to its deleterious nature. The product according to the invention will also be able to be used comfortably without any limitation in the fields where the use of quartz is limited, such as ceramic, glass, paint and plastic industries. As a result, it will be made possible to use the feldspar mineral, of which our country holds 14% of the worldwide reserve, in new fields and to also increase the export figures of said mineral.

[0010] Object of the Invention

[0011] An object of the invention is to develop a fine product with quartz and feldspar contents, said product comprising a quantity of respirable silica that does not pose a health risk according to the standards and further possessing the technical properties similar to those of the fine quartz products comprising a quantity of respirable silica that poses a health risk according to the standards, i.e., to develop a health and environment friendly product alternative to the purified fine quartz.

[0012] Another object of the invention is to develop a product, which, owing to possessing the same technical properties as those of the purified fine quartz and having no adverse health effects, is able to be used without any limitation in the fields where the purified fine quartz, due to being deleterious to health, may not be used or may be used only in limited quantities. Another object of the invention is to enable the feldspar mineral, which has technical properties similar to those of the quartz mineral and which at the same time is health and environment friendly, to be used in the fields where the fine quartz is needed due to its technical properties, i.e., to provide new fields of use for the feldspar mineral.

[0013] Another object of the invention is to utilize the natural raw material sources such as quartz and feldspar in many fields in an efficient and sustainable manner and without harming human health and environment.

[0014] Description of the Invention

[0015] The subject of the invention relates to a health and environment friendly fine product with quartz and feldspar contents, said product comprising a quantity of respirable (crystalline) silica that does not pose a health risk according to the standards, i.e., 0.3- 1% by weight respirable (crystalline) silica, and further possessing the technical properties similar to those of the fine quartz-based products comprising a quantity of respirable silica that poses a health risk according to the standards.

[0016] The product according to the invention basically comprises 10-50% by weight ground feldspar and 50-90% by weight ground quartz. The ground quartz comprises a quartz phase at a ratio of 98.50-99.00% by weight and the ground feldspar comprises a quartz phase at a ratio of 3-5% by weight.

[0017] In a preferred embodiment, the product according to the invention comprises 10% by weight ground feldspar and 90% by weight ground quartz.

[0018] In another preferred embodiment, the product according to the invention comprises 30% by weight ground feldspar and 70% by weight ground quartz.

[0019] In another preferred embodiment, the product according to the invention comprises 50% by weight ground feldspar and 50% by weight ground quartz. As a result of the XRD analysis performed on this product, the product was found to comprise a quartz phase at a ratio of 52.20% by weight and a feldspar phase at a ratio of 47.80% by weight. This result is provided herein in order to enable it to be understood that the product is possible to be developed without any problem occurring in the manufacture.

[0020] Within the scope of the studies conducted to obtain the finished product, quartz and feldspar, which were of the same size, were mixed according to different proportions and the variation in the respirable crystalline silica content of the mixture depending on the changing ratio of feldspar was examined. In order to determine the respirable crystalline silica content, the standards EN 689, EN 1232 and EN 481 and the SWeRF method are used by the workgroups, including European Industrial Minerals Association (IMA-EUROPE). According to the method, first the sampling is performed. Subsequently, the sample is subjected to particle size analysis conducted via both sedigraphy and laser diffractometer devices. Concordantly, the XRD mineralogical analysis is performed to quantitatively determine the respirable crystalline silica content. At this step, both the measurement is made via the Rietveld method provided with the device and the intensities of the quartz peaks obtained with the device in the previous calibration are observed, and the approximate value is checked based on the calibration. The determination is made via an approximation based on this value.

[0021] The studies were conducted with the sample mixtures comprising 15-micron quartz and 15-micron feldspar, 45-micron quartz and 45-micron feldspar, 63-micron quartz and 63- micron feldspar, 100-micron quartz and 100-micron feldspar, and 200-micron quartz and 200-micron feldspar, where each sample mixture comprises different ratios of quartz and feldspar. These mixtures were compared to the conventional products not comprising feldspar and it was found that the mixtures comprising feldspar had a proportionally lower crystalline silica phase. For the mixture comprising 100% by weight quartz with the size of 25 microns, the respirable crystalline silica content is measured as 20% by weight according to the SWERF method. For the quartz-feldspar mixture comprising 50% by weight feldspar with the same size, the respirable crystalline silica content is measured to be below 1% by weight according to the SWERF method. By increasing the feldspar content, the crystalline silica content of the finished product and the risk for the crystalline silica to adversely affect the health is reduced, said reduction being also dependent on the size. According to the standard, a product with a respirable crystalline silica content measured below 1% by weight is not subject to the risk classification, the hazardous class label is not used on the packaging of the same, and such a product does not pose a health risk in case of use.

[0022] According to the standard, a product with a respirable crystalline silica content in the range of 1-10% by weight carries a second class risk. In this case, the product causes the damage in the lungs in cases of prolonged or repeated exposure.

[0023] According to the standard, a product with a respirable crystalline silica content of above 10% by weight carries a first class risk. In this case, the product causes the damage in the lungs in cases of prolonged or repeated exposure.

[0024] As a result of the comparison of the measurement results with the standards, it was found that the respirable crystalline silica contents of all the alternatives of the product according to the invention are below 1% by weight and accordingly, the product is not included in any risk class.

[0025] In order to enable a better understanding of the invention, the results of the particle size analysis performed for the embodiment of the product according to the invention comprising 10% by weight feldspar are provided as an example. The data obtained from the analysis are entered in a table in accordance with the standard EN 481 and the value SWeRF, referred to as the respirable crystalline silica value, is calculated. As a result of the analyses, the product was found to comprise 0.11% by volume particles with the size of 2 microns, 0.32% by volume particles with the size of 2.70 microns, 0.8% by volume particles with the size of 5 microns, 1.04% by volume particles with the size of 7.5 microns, 1.25% by volume particles with the size of 10 microns, 12.09% by volume particles with the size of 63 microns, 18.19% by volume particles with the size of 74 microns, 22.12% by volume particles with the size of 80 microns, 29.14% by volume particles with the size of 90 microns and 99.57% by volume particles with the size of 300 microns.

[0026] The finished product accordingly comprises the particles with a size distribution range of 2-400 microns. That the size and the quantity of the respirable crystalline silica were measured at the levels not posing a health risk even in the product with the lowest content of feldspar demonstrate that the measured properties of the respirable crystalline silica would be even lower than these values in the alternative embodiments with higher feldspar contents.

[0027] The range of 10-50% by weight given for the content of feldspar is rather critical for producing the technical effect of the invention. The respirable crystalline silica content of the product is measured at a value posing a health risk in case the content of the feldspar used is below 10%, whereas a finished product with a feldspar content of above 50% by weight, will, due to the decrease in the quartz content of said product, be unable to exhibit the properties similar to those of the purified quartz- comprising products and thus the fields of use for such a product will remain limited. Therefore, said identified content range is critical for the solution of the technical problem. It was found out as a result of the analyses that the product has a size distribution similar to those of the products with high content of respirable crystalline silica used according to the state of the art and that it will be possible to use the product in the processes requiring the use of a fine product, such as the production of the dressed stones and the polymers.

[0028] The subject of the invention further relates to a method for obtaining said product, said method basically comprising the step of mixing the quartz ground via standard grinding methods and the feldspar ground via standard grinding methods for 5-60 minutes with the help of a multi-axis mixer on a dry mix line.

[0029] Before being mixed with feldspar, the raw quartz is enriched by means of the processes such as triage, magnetic separation and optical separation under the existing plant conditions, and is then crushed, passed through the sieves, fed into a mill, dried and subjected to grinding and separation process, purified in the bioleaching and / or hydrometallurgical leaching units if necessary based on the purity degree, washed, and dried. The purified quartz obtained in this way is ground in a high-speed grinder in order to obtain the fine quartz, after which the fine fraction is separated and removed.

[0030] As a result of mixing the fine-sized quartz and the feldspar according to certain proportions, the disclosed product has a lower respirable crystalline silica content compared to the respirable crystalline silica content of a certain quantity of fine quartz used according to the state of the art and thus poses no health risk according to the standards, but may still possess the technical properties similar to those of the fine purified quartz used according to the state of the art. While the respirable crystalline silica content of the conventional products with a high content of fine quartz is in the range of 15-20% by weight, the ratio of the respirable crystalline silica content varies in the range of 0.3-1% by weight, depending on the feldspar content, in the product comprising 10-50% by weight feldspar. Accordingly, the quartz-comprising fine product according the invention, which has no adverse effect on the health, may be used also in the fields such as polymers, paints and plastics, without any health concern. What is aimed with the invention is to bring together two different products of same size, one with a high quartz content and the other (feldspar) with a low quartz content, and to thereby reduce the risk.

Claims

CLAIMS1. A quartz- and feldspar-based mineral product characterized in that the mineral product comprises 10-50% by weight ground feldspar and 50-90% by weight ground quartz so as to have a final respirable crystalline silica content of 0.3-1% by weight and at the same time has the same properties as those of the purified quartz-comprising mineral products.

2. A product according to Claim 1 characterized in that the product comprises 10% by weight ground feldspar.

3. A product according to Claim 1 characterized in that the product comprises 30% by weight ground feldspar.

4. A product according to Claim 1 characterized in that the product comprises 50% by weight ground feldspar.

5. A product according to any one of the preceding claims characterized in that the ground quartz comprises a silica phase at a ratio of 98.50-99% by weight.

6. A product according to any one of the preceding claims characterized in that the ground feldspar comprises a silica phase at a ratio of 3-5% by weight.

7. A product according to any one of the preceding claims characterized in that the product comprises the particles with a size distribution range of 2-400 microns.

8. A method for obtaining a quartz- and feldspar-based mineral product characterized in that the method comprises the step of mixing the ground quartz at ratio of 50-90% by weight based on the weight of the product and the ground feldspar at ratio of 10-50% by weight based on the weight of the product for a duration in the range of 5-60 minutes with the help of a multi-axis mixer, so as to have a final respirable crystalline silica content of 0.3-1% by weight.