Foram investigados a mineralogia e o beneficiamento dos caulins do Rio Capim e Jari, com ênfase no alvejamento por lixiviação redutora do ferro. Foram avaliados três diferentes sistemas de redução: ditionito de sódio + sulfato de alumínio, dióxido de enxofre + alumínio em pó e dióxido de enxofre + zinco em pó. O caulim do Jari é constituído de caulinita, dickita, quartzo, anatásio, hematita, zircão e ilmenita. O do rio Capim tem ainda magnetita e ferro na estrutura da caulinita. É necessário usar separação magnética de alto gradiente antes da lixiviação. No caulim do rio Capim as impurezas são descartadas no desareamento. No Jari o redutor mais eficiente foi s'O IND.2' + 'ZN' e s'O IND.2' + 'AL', elevando a alvura de 79,9 para 87,5 ISO. O rio Capim responde melhor a lixiviação fornecendo produtos com alvura superior a 86% com qualquer dos três redutores estudados. S'O IND.2' + 'AL' ou 'ZN' fornecem produtos com 87,6% a partir de uma alimentação com 83,3%, sem necessidade de separação magnética previa.

Mineralogical characteristics and beneficiation aspects related to kaolin from Rio Capim and Morro do Felipe were studied. Emphasis was set on the bleaching aspects by means of reductive leaching of iron by three reducing systems, namely sodium dithionite plus aluminum sulfate; sulphur dioxide plus aluminium poder and sulphur dioxide plus zinc powder. Characterization studies provided the following conclusions: i) Morro do Felips kaolin mineral assembly is kaolinite, dickite, quartz, anatase, hematite, zircon and ilmenite; ii) Rio Capims kaolin mineral assembly comprises kaolinite, dickite, quartz, rutile, anatase, muscovite, hematite, magnetite, ilmenite, zircon and tourmaline; iii) The iron associated to kaolinite structure in the Morro do Felipe kaolin was detected by electronic paramagnetic ressonance and showed that high gradient magnetic separation should be carried out prior to leaching in order to obtain higher brightness levels (greater than 87.0% ISSO) in the products of beneficiation; iv) In the Rio Capim kaolin, the impurities which affected brightness most (magnetite, rutile, anatase, ilmenite and mica) were easily discarded in the desanding operation, thus favouring the bleaching step. As shown by characterization studies, magnetic separation proved to be a necessary operation in the beneficiation scheme for the Morro do Felipe ore.The reducing systems SO2 + Al and SO2 + Zn were the most eficiente, as the brightness of the products obtained improved from 79.9% up to 87.5% ISSO, close to minimum standards for coating applications in the paper industry. Out of the three reducing systems, SO2 + Zn proved to be the most suitable for bleaching purposes. It must be pointed out, however, that elementary zinc normally presentes environmental problems, due to the fact that it is a metal with a tendency to deposition and accumulation. The kaolin from Rio Capim is more amenable to bleaching than that from Morro do Felipe. Brightness numbers above 86.0% were easily achieved without needing a magnetic separation step prior to bleaching with all three reducing systems. Again in the case of this kaolin, the systems which used sulphur dioxide proved to be more suitable than sodium dithionite for bleaching, since products with 87.6% of brightness were obtained from a feed which scored 83.3% in this quality control variable.