Miljøprojekt, 1098 – Miljøstyrelsen og MAN B&W Diesel A/S - Karakterisering og nedbrydning af organiske indholdsstoffer i furansand fra støberier

Miljøstyrelsen og MAN B&W Diesel A/S - Karakterisering og nedbrydning af organiske indholdsstoffer i furansand fra støberier

English Summary

Introduction

Despite comprehensive internal reuse of moulding sand, the Danish metal casting foundries produce considerable amounts of spent sand. The amount of spent surplus sand is in the order of 80,000 tonnes a year, with 20,000 tonnes being spent sand from metal casting foundries using chemically bonded sand. Due to a content of phenols, aromatic hydrocarbons and other organic compounds, the main part of the chemically bonded spent sand is disposed of at landfills.

Reuse of moulding sand based on fractionating the sand in the production process reduces the total amount of spent sand to a minimum. The total amount of spent sand is still of a magnitude where the use of spent sand in e.g. construction practices is relevant.

The project

The purpose of this project is to make a physical and chemical characterization of five fractions of chemically bonded spent sand from the metal casting foundry at MAN B&W Diesel A/S at Frederikshavn, Denmark. Based on chemical analyses of sand from the five fractions of spent sand and a study of the circulation of moulding sand in the foundry, the amount and chemical composition of each of the five fractions have been described.

Furthermore, the purpose of the project has been to identify remediation technologies suitable for reducing the content of organic compounds in the spent sand, and to establish documentation for simple treatment of the used sand based on laboratory examinations.

Results

The study of the circulation of moulding sand in the foundry at MAN B&W Diesel A/S at Frederikshavn has revealed that the spent sand could be divided into five fractions with homogenous chemical composition. The five fractions of spent moulding sand make up approximately 85 % of the total amount of used sand in the foundry. Some of the five fractions have a high content of dust.

Two fractions from the cleaning of goods have a major content of heavy metals and minor content of organic compounds, while a fraction from the reclaiming process has a minor content of heavy metals and a major content of organic components. The two last fractions of spills and sand from cleaning of machinery have minor contents of heavy metals and moderate contents of organic compounds.

The content of heavy metals includes chromium, cupper, nickel and zinc, and the content of organic components includes p-toluenesulfonic acid, furfuryl alcohol, formaldehyde, phenols, BTEX, naphthalene and methylnaphthalenes. Generally, there is no significant content of polycyclic aromatic hydrocarbons (PAHs) in the five fractions of moulding sand.

Fractions with a high content of freshly made moulding sand (spills etc.) have major content of organic components, while fractions from cleaning of goods have a major content of heavy metals, probably due to the content of particles from the steel blasting process.

Generally, the concentrations of heavy metals in the spent sand are lower than the Danish EPA Soil Guidance Values, except for the fractions from the cleaning process, where the content of nickel is above the Soil Guidance Value. The contents of BTEX and naphthalene are generally above the Danish Soil Guidance Values.

The identified organic components are all soluble in water and expected to be biological degradable in aerobic conditions, though the information regarding biological degradation of p-toluenesulfonic acid is sparse. The environmentally most critical groups of components identified in the spent sand from the foundry are the BTEX and the phenols, as well as the components p-toluenesulfonic acid and furfuryl alcohol.

The fraction of spent sand from spills etc. comprises an amount of approximately 34 per cent of the total amount of spent sand from the foundry. This fraction has a low content of heavy metals and a moderate content of organic components, and was selected for further examination of degradation of the organic components in the spent sand.

In the laboratory, an examination was made of the effects of addition of water, air and inoculation with activated sludge to the fraction of spent sand from spills etc. The setup was followed during a period of 14 weeks.

The results of the laboratory tests show that the concentration of p-toluenesulfonic acid is high, and no degradation has been observed during the 14-week period. The concentrations of benzene, xylenes and naphthalene are all at a low level, and no significant reduction in the concentrations has been observed.

On the other hand, the concentrations of formaldehyde, furfuryl alcohol and phenols obviously fall to a lower level, but since no effect of inoculation with activated sludge has been seen, the reduction in the concentration of these components is expected to be a result of ongoing polymerization of resin in the spent sand.

At the end of the period of 14 weeks, the concentrations of phenols and furfuryl alcohol rise in the inoculated test setup. These compounds make up the basic structure of the high molecular resin, and the rise in the concentrations of these compounds could be due to a start in the degradation of the resin.

Conclusions

The project has revealed that spent sand from a metal casting foundry could be divided into five fractions, each with homogenous chemical composition. These fractions of sand are contaminated either with heavy metals or with organic compounds used to make the high molecular resin in the moulding sand.

The organic components in the five fractions of spent sand from the foundry at MAN B&W Diesel A/S at Frederikshavn are mainly p-toluenesulfonic acid, furfuryl alcohol, phenol and formaldehyde. Low contents of benzene, toluene, xylenes, naphthalene and methylnaphthalenes have been identified in the five fractions, but no significant content of polycyclic aromatic hydrocarbons (PAHs) has been observed.

The effects of simple treatment of spent sand with water, air and inoculation with activated sludge have been followed during a period of 14 weeks. The conclusions of the degradation test using simple techniques are no observed degradation regarding the organic components benzene, toluene, xylenes, naphthalene and p-toluenesulfonic acid. A lowering in the concentration of phenols, furfuryl alcohol and formaldehyde is expected to be due to ongoing polymerization of resin in the spent sand.

At the end of the period of 14 weeks, the concentrations of phenols and furfuryl alcohol increase in the inoculated test setup. It is concluded that the increase in the concentrations of these compounds could be due to a start in the degradation of the resin, due to the fact that these compounds make up the basic structure of the high molecular resin.

The results of the project show that the investigated fraction of spent sand has a content of organic components, which generally shows no significant reduction in concentrations when treated with simple techniques such as wetting, venting or inoculation with micro organisms.