Estudo avaliativo sobre a corrosividade de solos amazônicos por meio de análises geotécnicas, químicas e microbiológicas

Abstract

According to a study conducted in 2015 by the International Zinc Association (IZA) and USP, it is estimated that Brazil spends around R $ 236 billion on the replacement of equipment caused by corrosion. Several methods have been proposed to study and monitor this process. However, treating soil as a participant agent is still poorly considered. The presence of microorganisms in which a duct or structure is exposed, given the variety of environments that may present colonies of bacteria, fungi or algae may represent one of the major industrial problems of today. In this work the susceptibility of AISI 1020 steel to corrosion in contact with the representative soil of the Amazon region was studied, collected at points of exit from the soil. The techniques used for the soil were: Chemical (DRX, FRX, EAA, IV-TF, MEV, pH and total acidity), Geotechnics (limits of liquidity and plasticity, grain size and specific grain mass) and Microbiological seeding, isolation and characterization through pH, temperature, Gram staining, chemical testing, motility, nitrate reduction, oxidase and catalase tests. For steel, it was used: Chemical (FRX, EAA, MEV) and corrosion rate. The chemical characterization showed a clay soil, with the predominant presence of clayey kaolinite, with acid pH. The LL resulted in 83%; LP, 41%, showing an IP = 42%. With these parameters, it was observed that the studied soil has a high humidity retention. These conditions favor the presence of microorganisms such as fungi and bacteria. Among the bacteria present, Acidithiobacilus thiooxidans and Acidithiobacilus ferroooxidans were identified according to Holt (1994). The chemical and metallographic characterization of the steel confirmed that the steel used was AISI 1020. The SEM analysis showed microbiological corrosion on the analyzed surface. The corrosion rate for this type of soil was high; and, the degree of soil aggressiveness was classified as severe, according to NACE parameters. The results indicated that a complete analysis of this medium is necessary to better understand its corrosive action and, subsequently, to choose the best way of protecting the buried material.