This study used iron-oxide-coated natural rock (IOCNR) an adsorbent of arsenic from real arsenic-bearing groundwater collected from the Lanyang Plain, North Eastern Taiwan. SEM and EDX were applied to characterize the as-prepared adsorbent. Batch adsorption studies were conducted at 25 +/- 2 degrees C.A 15 g L-1 dose of adsorbent removed similar to 75% of the total arsenic from the real sample when the initial arsenic concentration was 40 mu g L-1 and the pH was 7.5 (reduced to 10 mu g L-1, the maximum contaminant level (MCL)). The contact time was 6 h and the agitation speed 180 rpm. Adsorption followed the Langmuir isotherm and the maximum adsorptive capacity of IOCNR was 0.36 mg g(-1). The dimensionless parameter (R-L) and Gibbs free energy (Delta G degrees) changes suggested that the process is favorable and spontaneous. The adsorption process followed the first-order reaction kinetic model better than the other three kinetic models, and film-diffusion was the rate-limiting step. Arsenic removal efficiency of the exhausted and NaOH-regenerated IOCNR decreased in the second-cycle operation. Arsenic removal efficiency of IOCNR was comparable to that of the commercially available patented adsorbent LEWATIT FO36. (C) 2011 Elsevier B.V. All rights reserved.