Silica is one of the most abundant materials found in the earth. It is available in many forms, both crystalline and amorphous amongst which quartz is the most common naturally occurring variant. In many parts of the world, silica is the main constituent of sand and a critical constituent of Portland cement. Finely divided crystalline silica is toxic and longterm inhalation of it can lead to silicosis; an acute occupational fatal lung disease without any cure. Rapid urbanization and industrialization release significant amount of silica to the environment that is potent enough to harm the human population. Therefore, effective and easy determination of the amount of silica in industrial waste and construction site dust is important to understand the level of threat. For that purpose, we have successfully measured the amount of silica deposited in industrial glass microfiber filter papers and a construction site dust from a metro city using FTIR technique.
Materials and Methods:
For the preparation of a calibration curve, a standard CRM for quartz was used and analyzed using FTIR for 0.5, 1, 2.5 and 5 % quartz content respectively. KBr was used for the preparation of pellets and subsequent dilution. A Nicolet is-10 instrument from Thermo Fisher Scientific was used for the FTIR analysis.Two industrial micro fiberglass air filter papers and a blank micro fiberglass filter paper were ignited at 800°C for 3 hours and grinded in an agate mortar before mixing with KBr. These filter papers were procured from Micro Separations and were installed to measure the air quality at a village situated at an approximate distance of five kilometers from a thermal power plant. An arrangement was made to install the filter papers at a height of three to ten meters from the ground. The dust sample was collected from a mega construction site in a metro city and grinded in an agate mortar for the preparation of the KBr pellets.A characteristic peak for silica in was observed around 1081 cm-1 in the standard and the dust sample. In the case of filter papers, the peak was slightly broadened due to the presence of glass microfibers. A small shift towards the lower wavenumbers was also observed in case of filter papers which may be attributed to the presence of various metallic residues. Figure 1 represents the so generated four-point calibration curve. The results are summarized in table 1.
|Micro fibre glass air filter paper blank||0.81|
|Micro fibre glass air filter paper 1||0.41 (after blank correction)|
|Micro fibre glass air filter paper 2||0.18 (after blank correction)|
Figure 1: Calibration curve with different quartz concentrations
Figure 2: FTIR spectra of standard quartz.
Figure 3: FTIR spectra of the dust sample.
Figure 5: FTIR spectra of industrial glass microfiber air filter paper 1.
Figure 6: FTIR spectra of industrial glass microfiber air filter paper 2.
In this work presented herein, we have determined the amount of silica present in urban dust sample and industrial air filter papers using a simple and inexpensive FTIR technique. Our results show the presence of significant amount of silica in urban dust samples which can easily be airborne and escape to the nearby localities from the site of occurrence. On the other hand, though the silica concentration observed in the industrial filter papers is high but we cannot overlook the contribution of the ongoing construction in the village and other rural activities as the exhaust fumes from the power plant are expected to be free from silica after separation of fly ash and other precautionary measures.Long term exposure to silica is harmful yet it is unavoidable in urban and industrial area due to surge in construction and other developmental activities. Therefore, effective determination of silica and other pollutants is of significant importance to understand the level of threat on the basis of which concerned authorities would be able to take necessary steps.
Contributed by: Arijit Goswami & Satirtha Sengupta