Dust-raising behaviour and material composition of diatomaceous earths

Status:

completed 12/2001

Aims:

Diatomaceous earth comprises up to 20% quartz, depending upon the region in which it is extracted, and up to 70% cristobalite, depending upon the calcination/activation process. Diatomaceous earths are employed for example as filter media in the beverages industry, in particular in breweries. They are generally delivered to the breweries packed in sacks. In the breweries, the diatomaceous earth is mixed with water to form a suspension, which is deposited in filtering layers by means of which turbid matter such as yeasts is subsequently filtered out of the beer. Dust emissions must be anticipated during manual handling of the sacks, for example when the sacks are opened, when the diatomaceous earths are dumped into the mixing vat, and during disposal of the empty sacks. The need in the beverages industry for prevention measures (substitution, reduction of exposition) relating to contact with diatomaceous earths was investigated, in connection with the discussed classification of quartz and cristobalite as carcinogenic hazardous substances, launched by the institution for statutory accident insurance and prevention in the foodstuffs industry and the catering trade.

Activities/Methods:

The project examined both the material composition of different diatomaceous earths and filter substitutes, and their dust-raising characteristics. The analytical study of the material composition encompassed measurement of the fine dust component (respirable fraction) and the quartz and cristobalite components in the original substance and in the fine fraction. The dust-raising characteristics of the various samples were studied by means of a counterflow drop tube developed by the IGF hazardous substance research centre in Dortmund and an SP 3 sedimentation meter manufactured by Lorenz, Kattlenburg (Germany).

Results:

The samples differed, in some cases substantially, with regard to their material composition. The quartz and cristobalite content in the sample material ranged from approximately 2 to approximately 46%. Quartz contents of between < 1 and 64% were measured in the fine component. Quartz contents of < 1% were detected in the original sample and fine component of low-quartz/low cristobalite substitutes. These products can therefore be classified as "favourable" in terms of their material composition and the associated hazard potential. The diatomaceous earths demonstrated a low tendency towards dust release. In contrast, the low-quartz and low-cristobalite substitutes exhibited a substantially higher propensity to dust emission in the dust-raising tests. The dust-raising characteristics thus negate to some degree the benefits of the low quartz content.

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