Dispersantes químicos na análise granulométrica de latossolos

• Autor(a) principal: Mauri, Jocimar
• Data de Publicação: 2008
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5421
• topic: Dispersantes químicos; Solos; Análise granulométrica; Dispersing chemicals; Soils; Granulometric analysis; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

The most accurate textural analysis result is dependent on the soil sample s complete dispersal and maintenance of the dispersed phase s stability. The solution s high pH can be considered to be determinant in the dispersion of soils with pH dependent loads. Under the same pH and osmotic pressure conditions, the higher the ion s ionic hydrated radius, the more effective the clay dispersion will be, as a result of the increment of the diffuse double layer. Finally, the removal of cementing agents also increases soil sample dispersal. Thus, Na+ and Li+ compounds were tested as alternative dispersers against the solution NaOH 0.01 mol L-1, aiming to obtain a more effective dispersion so as to minimize the presence of pseudo-components, fundamentally pseudo-silt,in the granulometric analysis of Latosols. Samples of eight Latosols from the state of Minas Gerais were used, selected for presenting different materials of iron oxide origin and content. The treatments were arranged in a randomized block design, in an 8 x 2 x 7 factorial scheme, and three repetitions. The factors studied were the eight Latosol samples, removed from horizons A and B and seven dispersers. NaOH was used as a reference disperser, by additionally testing the solutions LiOH, NaClO, [NaClO + NaOH], [HCl + NaOH], (NaPO3)n and [(NaPO3)n + NaOH]. Mechanical dispersion was performed using a Wagner type rotatory agitator, regulated for 50 rotations during 16 hours. The alternative dispersers were compared with NaOH by means of the Dunnett test. Using the highest clay proportion to identify the dispersers effectiveness, none of them was equal to NaOH. Using the sign > to indicate greater effectiveness, the sequence determined was NaOH > [(NaPO3)n + NaOH] > [HCl + NaOH] > [NaClO + NaOH] > LiOH > (NaPO3)n > NaClO. Among the alternative dispersers, the [(NaPO3)n+NaOH] solution stood out, with results close to those of the reference disperser, showing the importance of increasing the pH up to values close to 12. The effectiveness of the other sodium solutions with high pH, [NaClO+NaOH] and [HCl+NaOH], was reduced by increasing the osmotic pressure of the solution, making soil sample dispersion difficult. LiOH was lower than the reference disperser. Such response is justified by the tendency of this alkaline cation to form covalent bonds that block negative electric loads of the clay exchange complex, leading to a decrease of the superficial load density. (NaPO3)n and NaClO were the least effective dispersers, due to the lower pH of their solutions. It can be concluded that the NaOH solution is the most effective in dispersing soil samples with clay presenting pH dependent cationic exchange capacity, favoring the increase of negative loads, repulsion between particles, and, consequently, soil sample dispersion with relatively low suspension osmotic pressure values.