Beneficiamento de uma argila tipo palygorskita da Bacia de São Luis-Grajaú, região de Alcântara (MA) e sua utilização como adsorvente de fósforo.

Abstract

The estimated contribution of the industry minerals in Brazil is about 70% of National Mineral Production Value. These minerals are important because of its diverse applications. Among them, in clay minerals group, there is palygorskite, which presents the requirements to join special clays group, once their occurrence is restricted. Thus, this new mineral occurrences deserve attention and further study. Adding to this, there is the fact in the Amazon region, as well as in most areas of tropical and temperate zones, the acidity is an important factor in land degradation and represent one of the major problems faced by agriculture. Acid soils have several limitations, which hinders the use of nutrients, requiring the addition of fertilizers, always aiming maximum efficiency. In this context, this study used a sample from the Bacia de São-Luis-Grajaú, Maranhão State, consisting of a mixture which is predominantly palygorskite and dolomite, approaching the existence of this new occurrence, suggesting a processing method and its application as phosphorus adsorbent, once dolomite is a pH soil corrector, while palygorskite has the function of nutrients carrier. First, chemical and mineralogical characterizations were performed, by XRD, XRF, SEM and separation of sand, silt and clay fractions. Sedimentation and phosphorus adsorption experiments were also performed, with determination of kinetic curve. After the analysis of XRD, results shown that the sample consists mainly of palygorskite and dolomite. Illite, chlorite and quartz are also presented. It was also possible to see that the different types of disaggregation used showed no significant differences in the diffractograms of the samples. The sand-silt-clay separation, although only based on the size of the material, showed a reasonable efficiency for material separation, as the sedimentation tests, where it was noticed that after a 24 hours period, dolomite had disappeared from the supernatant. Determination of kinetic curve revealed that the adsorption period of 2 hours is not sufficient for phosphorus adsorption, requiring 24 hours to reach the reaction equilibrium. Sorption tests showed efficiency higher than 91% of the initial phosphorus present in solution, and the maximum quantity adsorbed per gram of sample was 0.607 mg. The correlation with the adsorption isotherm models studied, showed better results for Langmuir-Freundlich isotherm, with correlation coefficient of 0.9993, which can be attributed to the fact that adsorption occurs in more than one layer.