Estudo de argamassas de revestimento com resíduo de scheelita

Abstract

The state of Rio Grande do Norte has a large concentration of scheelite, the main source of tungsten, an important chemical element for production in various industries. When extracting the raw mineral material, tons of residue are generated and lunges in the environment. This work aims to analyze the use of this residue as a substitute for sand in the formulation of coating mortars. Scheelite residue samples were collected in Brejuí mine, Currais Novos/RN, and after its initial characterization, it was observed the application of the thick residue in the mortars in study. Were analyzed mixing mortars by 1:1:6 (cement:lime:sand) and 1:3 (cement:sand), both in volume with percentages of 0%, 25%, 50%, 75% and 100% of the sand replaced by scheelite thick residue. It was used Portland cement CP II-Z 32 and CH-I hydrated lime with ratio water/cement between 0.18 to 0.16 and a consistency of 260 ± 5mm. Subsequently, the mortars were analyzed in the fresh state through the consistency testing, bulk density, water retention and incorporated air content and in the hardened state by the compressive strength test and tensile strength in bending, bulk density, water absorption by immersion, water absorption by capillary and dynamic modulus of elasticity. The experiments of initial characterization of the residue showed that the natural thick residue has a granulometric distribution very close to the natural sand, has a larger amount of fines and a specific mass higher than natural sand, which resulted to an improvement in mechanical resistance and dynamic modulus of elasticity. X-ray fluorescence (XRF) and x-ray diffraction (XRD) analyzes indicated a pozzolanic propensity of the scheelite residue, but the minimum parameters according to NBR 12653 (2014) to be classified as pozzolanic material were not achieved. In the fresh state, the mortars have improved water retention, allowing greater retention of kneading water. The bulk density presented higher results (about 5% higher) and the incorporated air content, smaller (about 2% lower) in relation to the reference mortar, resulting in dense mortars with less workability, compensated because the natural thick residue had a higher content of fines than sand. In the hardened state, the mechanical resistances recorded higher results. The best results for mortars with 100% replacement of the natural aggregate by residue and trace of 1:3. The bulk density in the hardened state kept the bulk density pattern fresh. And the water absorption by both immersion and capillarity were predominantly larger than the reference mortar. In this way, it is possible to affirm that the residue from the extraction of the scheelite is suitable for use in the manufacture of conventional mortars.