This work presents a study of arsenic adsorption kinetics and equilibrium on synthetic iron oxyhydrates and its extraction by bicarbonate solutions, as a model to explain the fast way for arsenic lixiviation from mining tailings by this mechanism. The arsenic adsorption on synthetic goethite and ferrihydrite showed a pseudo-first order kinetics, reaching the equilibrium in 6-7 days. The adsorption isotherms for arsenic on synthetic goethite and ferrihydrite carried out at different temperatures levels showed the same and maximum adsorption capacity of 15-18 mg/g, presented a best fit according to Langmuir Isotherm Model; 95% of arsenic adsorbed in these materials was extracted with bicarbonate solutions 0.5 M, pH 8.5 in 2 h. Approximately 25% of total arsenic present in the mine tailings was extracted by bicarbonate solutions in 6 h. The results suggest that in these tailings, there is an arsenic fraction bound to iron oxyhydrates that can be quickly lixiviated by bicarbonate solutions.