Removal of Arsenic and Iron from Acidic Water Using Zeolite and Limestone: Batch and Column Studies

Zeolite and limestone were tested for their capability of removing As and Fe from acidic water in batch and column experiments. Synthetic acidic water with 3 mg/L As and 50 or 100 mg/L Fe at pH = 2 was used in the column experiments. In the batch experiments, the As concentration, the mass of media, and the contact time were varied between 0.2 and 5 mg As/L, 0.5 and 50 g, and 0.25 and 42 h, respectively. Maximum As sorption capacity as indicated by the Langmuir model was 0.17 mg/g for zeolite and 1.3 mg/g for limestone, at 18-h contact time and 6.3 g/L medium concentration. Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses revealed that As and Fe were retained in zeolite at the end of the batch experiments. The main factors affecting As and Fe removal efficiency and pH raising capacity were the contact time and the media concentration. This was confirmed in the column experiments, since zeolite and limestone columns presented 99% As removal, under a hydraulic loading rate of 21.8 mm/day. However, limestone columns presented a higher Fe removal: 99 versus 73% for zeolite. The results indicate that limestone could be more appropriate than zeolite when As and Fe are present under acidic conditions, given its higher capacity to remove both As and Fe and to raise pH.