Procedimiento de síntesis de pigmentos ultramar

Procedimiento de síntesis de pigmentos ultramar por calcinación en una sola etapa y en ausencia de aire de una mezcla que comprende zeolita A, sulfuro de sodio y azufre, caracterizado por que: - la zeolita A se seca previamente hasta un contenido de agua inferior al 10 % en peso, preferentemente inferior al 1 % en peso, y - los reactivos de dicha mezcla son mezclados en ausencia de aire, y - el medio de reacción está exento de agua. The present invention relates to an ultramarine pigment synthesis process which includes a calcination step in the absence of air of a mixture including zeolite A, possibly sodium sulfide and/or sulfur, possibly hydroxide ions, and polysulfides of composition Na2Sn, n being a number greater than 1, the product resulting from the calcination reaction being cooled in the absence of air, leading to obtaining a raw product which includes the synthesized ultramarine pigment, polysulfides and possibly sulfur. The Na2Sn polysulfides taking part in the calcination reaction come at least in part from the recycling of the polysulfides and possibly of the sulfur present in excess in the aforesaid raw product.