Figure 4. Effects of initial solution pH on the removal of As(V) (a) and As(III) (b) (Experiment conditions: adsorbent dose  = 0.02 g 100 mL⁻¹, temperature  = 25±0.8°C, agitation speed  = 150 rpm, initial concentration  = 100 µg L⁻¹, contact time  = 14 h).