Лако-красочные материалы — производство

Ultramarine pigments have a unique safety record. No other pigment has had such long term and widespread human and environmental exposure without any reported instances of ill effect. The principle uses for ultramarine in earlier times constituted a world wide test of human safety since it was sold and used around the world as an additive for sugar, to produce a whitening effect, and as a clothes whitening agent for use in the household wash. Whole populations ate sugar regularly. The use of ultramarine for whitening clothes was, and still is, widespread. This represents a test of safety in human ingestion and skin contact on a grand scale. Their only known hazard is the evolution of hydrogen sulfide on contact with acid.

Tests sponsored by Reckitt’s Colors (now Holliday Pigments) confirm that acute oral toxicity in rats and mice (LD50) is greater than 10,000 mg kg-1. Fish toxicity (LC50 in rainbow trout) exceeds 32,000 mg L-1. Ultramarine is non-mutagenic, non-irritant, and non-sensitizing to skin.

There is no listed threshold limit value or maximum exposure limit for the pig­ment. Normal practice is to consider it a nuisance dust with TLV 10 mg m-3. The pigment is not listed as a dangerous substance in the EC nor in any similar national or international classification; neither is it classified as hazardous for disposal.

The production process evolves close to 1 t of gaseous sulfur dioxide and 0.3 t of water-soluble sodium sulfoxides for every metric ton of pigment produced. These must be disposed of in an environmentally acceptable manner. If the soluble salts are fully oxidized, they can be discharged safely into tidal waters. The legislation around the world requiring the reduction in discharges of sulfur dioxide has led to the demise of many ultramarine producers. The investment required is significant but can result in a dramatic reduction in the level of emissions. The solution implemented at the largest ultramarine factory in the world has reduced sulfur dioxide emissions by more than 99.5%. This is achieved by conversion of the SO2 to SO3 using a vanadium pentoxide catalyst and the subsequent condensation of the sulfur trioxide to produce very concentrated and pure sulfuric acid.

3.5.6