Zinc sulfide pigments

White pigments based on zinc sulfide were first developed and patented in 1850 in France. Although they are still of economic importance, they have continually lost market volume since the early 1950s when titanium dioxide was introduced. Only one modern production installation for zinc sulfide pigments still exists in the mar- 

The zinc-sulfide-containing white pigment with the largest sales volume is litho-pone [1345-05-7], which is produced by coprecipitation and subsequent calcination of a mixture of zinc sulfide [1314-98-3], ZnS, Mr 97.43, and barium sulfate [7727-43-7], BaS04, Mr 233.40. For standards, see Table 1 (Lithopone pigments Specification ). Pure zinc sulfide is marketed as Sachtolith. 

White zinc sulfide pigments maintain their market position in areas of use where not only their good light scattering ability but other properties such as low abrasion, low oil number, and low Mohs hardness are required. 

They are often produced from many types of industrial waste. This recycling relieves pressure on the environment, as these materials would otherwise have to be disposed of. 

Some physical and chemical properties of ZnS and BaS04 are given in Table 19. 

The starting material is an anatase pigment or a Ti02 hydrolyzate, which is calcined with oxides of transition metals to form chromium mtile or nickel rutile pigments (see Section 3.1.3.). 

Nanostructured Ti02 particles (particle size 5-50 nm) are used as sunscreens in the cosmetic industry. Nanosized Ti02 is an effective absorber of UV-B (280-320 nm) and UV-A radiation (320-400 nm). Because ofits small particle size, itappears transparent [2.70]. Intensive research work is in progress worldwide aimed at utilizing the photoactivity of Ti02. Titanium dioxide catalyzes the decomposition of organic compounds in wastewater [2.71]. 

Generally, inhalation of smaller particles into the lung is more detrimental compared to larger particles. But there are no known specific chemical reactions of Ti02 resulting in inflammation [2.68]. 

A more detailed outline of the toxicological effects of Ti02 with a helpful list of labeling, registration and permission requirements can be found in Ref [2.68]. 

---

Table 19. Properties of the components of zinc sulfide pigments...

Raw Materials. The source of zinc can be zinc oxide from a smelter, zinc dross or sweepings, ammonium chloride slag from hot dip galvanizing, or liquid waste such as pickle liquors from galvanizing plants. Variations in the price of zinc have a large effect on the economics of zinc sulfide pigments. 

Most of the heavy-metal impurities present in zinc salt solutions must be removed before the precipitation reaction, or these form insoluble colored sulfides that reduce the whiteness of the zinc sulfide pigment. This end is usually achieved by the addition of zinc metal which reduces most heavy-metal ions to their metallic form. The brightness of zinc sulfide can be improved by the addition of a small amount of cobalt salts (ca 0.04% on a Co/Zn basis) (20). Barium sulfate [7727-43-7] formed in the first step is isolated and can be used as an extender. 

White pigments the optical effect is caused by nonselective light scattering (examples titanium dioxide and zinc sulfide pigments, lithopone, zinc white)... 

Some physical and chemical properties of ZnS and BaS04 are given in Table 2.10. Tab. 2.10 Properties of the components of zinc sulfide pigments. 

Total world production of zinc sulfide pigments in 2003 was 260 xlO t. This was subdivided as follows (10 t) ... 

Methyl hydroxyethylcellulose Zinc sulfide pigment, leather cloth... 

Ultramarine violet Wollastonite Zinc sulfide pigment, paints/coatings Ferric oxide Kaolin Methyl hydroxyethylcellulose Pigment green 36 Pigment orange 36... 

Pigment yellow 151 Pigment yellow 154 Sodium alumino sulfo silicate Talc Titanium nickel yellow Wollastonite Zinc sulfide pigment, plastics industry Pigment orange 75 pigment, plastics emulsion paints Polystyrene pigment, polishes Titanium dioxide... 

Zinc Suifide. Zinc sulfide pigments were developed in 1850. They still have some use in plastic because they are less abrasive and can have a smaller particle size. However, after the introduction of titanium dioxide in the 1950s they have continually lost market share. 

The rarity of matraite means that it is unlikely to have been used as a pigment. However, its pure synthetic analogue, zinc sulfide (q.v.), may be encountered in the manufacture of zinc sulfide pigments. 

---