Otimização do processo produtivo de superfosfato a partir da avaliação da conversão e do consumo energético

Abstract

Phosphate rock is one of the raw materials used in the manufacturing process of simple superphosphates. For an adequate evaluation of the productivity of superphosphates, it is necessary to quantify the phosphorus present in the rock, which is determined and expressed as phosphorus pentoxide equivalent (P2O5). This variable, in turn, may be strongly dependent on the origin of the phosphate rock. However, the use of phosphorus present in the rock has low solubility with regard to plant absorption, making its direct application in agriculture unfeasible. In view of this, it is necessary to carry out a chemical treatment based on the use of strong acids, increasing its bioavailability. In this context, the present work aims to evaluate the influence of granulometry, acidulation ratio and type of phosphate rock on energy conversion and consumption. Two types of phosphate rocks were used: one of national origin (Serra do Salitre) and another of African origin (Egypt). Both were characterized in terms of their reactivity in the acidulation process, fluidity, density, moisture, ease of grinding the rock and the phosphorus and sulfur pentoxide content, as well as the presence of impurities. In order to evaluate the reactivity of the rock, bench tests were conducted to determine the optimal acidulation ratio, which corresponds to the experimental condition capable of promoting the highest reactional conversion without a large excess of free acidity. With the data obtained in the grinding and acidulation steps, this study suggests that the different types of rocks have advantages and disadvantages depending on the applicability. The Egypt rock has six times more impurities in the form of heavy metals (Fe2O3 and Al2O3), when compared to Salitre. The acidulation ratio (AR) of 0.60 showed a conversion of 94% in 4 days for the Egypt rock, while, for the same RA, the Salitre rock took 24 days to reach the milestone of 94% conversion. It is recommended to choose the type of rock according to each specific need. This study, by proposing the characterization of different phosphate rocks and optimization of process variables, intends to provide information that can be valuable in making commercial decisions for the acquisition of raw materials, saving time for adapting the plant to the rock.