Development of inorganic binder systems to minimise emissions in ferrous foundries

Abstract

A series of sands with binders based on synthetic resins, which ensure the achievement of some molding sand parameters better than sands with a natural clay binder, do not meet the required expectations related to the impact on the surrounding environment. These include three main classes of sands in which organic binders based on alkyd, phenol-formaldehyde, furan and urea-formaldehyde resins are used. Molding sands subjected to high temperatures of liquid metal generate a number of harmful and even dangerous substances (carcinogenic and/or mutagenic) from the group of benzene, toluene, ethylbenzene and xylenes (BTEX) and polycyclic aromatic hydrocarbons (PAHs). Research carried out as part of the LIFE Green Foundry Project (LIFE17 ENV/FI/000173) concerned the analysis of various types of molding sands in terms of emissions of BTEX and PAHs gases and other compounds (SO2, CO, CO2 and NOx) formed in the process of pouring the mold with liquid metal. In the article, particular attention was paid to the differences in the amount of emitted BTEX and PAHs compounds for two types of sands with organic resins: furan resin (code MF) and phenol-formaldehyde resin (code MA), for which the influence of the regenerate addition on the above values was additionally examined. Three sands with inorganic binders, including 2 binders on water glass base (code MI and code MC) and 1 binder on aluminosilicate base (code MG), and greensand with activated bentonite and coal dust (code MB) were also tested. A comparative analysis of the results evaluated against sand with resin (code MF) containing 85% free furfuryl alcohol, conventionally accepted as a reference sand mix, was performed.It was noted that for a foundry with a uniform (according to the BREF – Best Available Techniques Reference Document for the Smitheries and Foundries Industry) system of molding sands, the obtained Loss on Ignition (LOI) results of the reclaimed fraction compatible with the used molding sand can be used to develop an empirical relationship that allows predicting the approximate content of a given harmful substance (PAHs, BTEX groups) in the molding sand, which makes it easier for the foundry to decide on the need to conduct more advanced tests.The research justifies the opinion about the possibility of reducing the harmful impact of an iron alloy foundry on the surrounding environment by replacing molding sands with organic binders by molding sands with inorganic binders.