Adsorption and Desorption of Arsenate in Different Soils and Gold Mining Substrates of Minas Gerais State, Brazil

• Published in: Journal of soils and sediments 2004, Vol.4 (3), p.163-169
• Main Authors: Ribeiro, Emerson S., Dias, Luiz E., Alvarez, Víctor Hugo V., Lynch, Leila S.
• Format: Article
• Language: English
• Subjects: Adsorption; Analytical methods; Anions; Anthropogenic factors; Arsenates; Arsenic; Availability; Binding energy; Bio-assays; Bioassays; Buffers; Capacity; Clay; Clay soils; Desorption; Dynamics; Environmental impact; Filter paper; Gold; Immobilization; Lability; Materials; Methods; Mitigation; Natural environment; Plants; Resins; Samples; Sandy soils; Soil; Soil dynamics; Soil solution; Soils; Sorghum; Substrates; Sulphides; Thermodynamics; Toxicity; Tropical environments; Tropical soils
• ISSN: 1439-0108; 1614-7480
• DOI: 10.1007/BF02991134

BackgroundArsenic (As) availability in natural environment is related to the element’s adsorption and desorption processes in soils. Total As is better related to available As in temperate soils than in tropical soils. In tropical soils, total As is not very significant in terms of availability, therefore justifying the necessity for studies into As dynamics. Knowledge of As dynamics in soil as well as development of new analytical methodologies involving tropical soils are insufficient and necessary for future mitigation projects.ObjectiveThe objectives of this study were: (1) To adjust methodologies which may assist in understanding arsenate dynamics in tropical soils and substrates; (2) To evaluate the adsorption and desorption of arsenate in soils and substrate samples, and to find a minimum value of arsenate available in soil which is lethal to sorghum plants.Material and MethodsSamples of three soils from Minas Gerais State (YL, RYL, and CS) and two sulfide substrates of gold mining (B1 and B2) were used in the assays. All the material was physically and chemically characterized. Remaining As (As-rem) and remaining P (P-rem) of each material, along with MACP and MACAs (using the Langmuir isotherms), were obtained. After agitation to obtain MACP and MACAs, arsenate was extracted by anionic resin and Mehlich-III to evaluate arsenate desorption of the material retained on the filter paper. Subsequently, arsenate desorption curves for the different materials were obtained, and arsenate availability was determined through a bioassay with sorghum plants. Samples of soils and substrate B1 were incubated with six levels of As doses. Plants were grown under greenhouse conditions for 30 days. The plants were then harvested, dried and weighed. Available As in the soils and substrate was determined by Mehlich-III.Results and DiscussionsAs-rem level decreased from YL (sandy) to RYL (clayey) soil samples, which always showed lower values than P-rem. Among the soils and substrates evaluated, RYL showed the highest MACAs and MACP, followed by CS, YL and Bl. The results were in accordance with the values observed for As-rem and P-rem and confirm the idea that the ability of the assayed materials to remove As from the soil/substrate solution is higher than the ability to remove P. On the other hand, the binding energy (a) between soil/substrate and As is weaker than the binding energy of P. Given the fact that the studied soils present a real ability to remove As from