GB799202A - Improvements in or relating to the preparation of iron derivatives - Google Patents

Abstract

An iron derivative, suitable for use in paints, is obtained by mixing an alkali or alkaline earth carbonate with ferrous sulphate under dry conditions, both having a grain size below 200 mesh and the ratio by weight of the sulphate to carbonate being between 1 : 4 and 4 : 1. The mixture is then allowed to absorb atmospheric moisture for between 4 and 7 days, and is then stored tightly packed in an enclosed space at room temperature for about 3 weeks. The mixture is then dried and powdered to below 200 mesh. Up to 15 per cent by weight, based on the sulphate, of the iron derivative from a previous batch, or of another nucleous such as china clay, silica, titania, yellow earth ochre, green, blue or black pigment, may be added to the original mixture. The product may be ground and washed with water, or preferably first with water containing up to 1.5 per cent of sodium silicate or an anion-active wetting agent, e.g. "Teepol" (Registered Trade Mark) and then with pure water or water containing sodium thiosulphate, prior to drying. The carbonate used is preferably calcium carbonate, which may be added in the form of chalk, in which case the mixture may be screened to remove impurities such as silica before drying. The product may be calcined to give anhydrous ferric oxide.