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The use of harmful metals is being restricted worldwide by various government regulations in an attempt to reduce and control the environment pollution. However, the lack of alternatives necessitates the use of materials containing harmful metals in many fields [1, 2]. For example, inorganic color pigments with metals such as mercury, cadmium, and lead exhibit good properties, including high stability against radiation, heat resistance, coloring visibility, and low cost [3-5]. In addition, because of their low coloring and opacity, oxide pigments are not suitable for incorporation in paint and plastics [6]. Sulfate and nitrate pigments have lower heat resistance than oxide pigments and also require harmful and/ or combustible gas to synthesize. Furthermore, it is difficult to obtain sulfide and nitrate pigments with repeatability [7, 8]. Therefore, novel inorganic pigments with suitable properties and facile production methods are demanded. Several kinds of inorganic red pigments are available for use, e.g., red iron oxide, red lead, cadmium red, vermilion, and cinnabar [9-12]. However, they all suffer from several disadvantages. For instance, red iron oxide exhibits only limited colorfulness, while other pigments contain harmful metals such as lead, cadmium, and mercury. Therefore, a novel red pigment that is economical and does not contain any harmful metals is required. We focus on the natural ore natrophilite (NaMnPO4), because it contains low-toxicity metals [13, 14]. Natural ores have high stability against radiation and heat resistance. Furthermore, they exist in solid phase, which allows applications in plastics, paint, ceramics, etc. Natrophilite contains bivalent manganese ion. The valence of manganese is important to prepare these novel red pigments. Here, novel inorganic red pigments NaMnPO4, imitating natrophilite, were synthesized by heating a mixture of raw materials. The products were subsequently analyzed.

Synthesis of novel red phosphate pigments from manganese carbonate to imitate natrophilite