Crystalline hydrous titanium (IV) oxide (CHTO): An arsenic (III) scavenger from natural water

Abstract

Arsenic contamination (>10 ppb) in groundwater poses a risk to public health globally. The problem is apparently the greatest in the Bengal basin of the Ganga River. As(III) is a major contaminant in anoxic groundwater. Here, a systematic report on As(III) removal using synthetic crystalline hydrous titanium(IV) oxide (CHTO) is made. Absolute As(III) sorption capacity is 72 to 75 g kg -1 at a pH of 7.0. CHTO has nearly the same sorption density in the pH range of 6.0 to 9.0. Use of pre-dried CHTO above 350°C shows a decrease in sorption density from 11.50 (±0.10) to <9.0 mg g -1 . Approximately 70% of As(III) sorption takes place within 0.5 hour. Interfering effect studies of some ions show a poor effect on the sorption process except for HCO - 3 . As(III) sorption follows the Lagergren first-order kinetic model and the sorption data fit the Freundlich and Langmuir isotherms well. Batch and column methods for regeneration of arsenic rich CHTO with 1.0 M NaOH solution show ∼ 90% and 75 to 80% regain of its initial efficiency, respectively. Flow-rate and bed depth variation effects on As(III) removal from a spiked (500 μg l -1 ) natural water are reported systematically. Lab-bench mini-pilot scale application of a fixed-bed (bed volume=30.0 cm 3 ) CHTO column is reported at a down flow-rate of 33 to 34 B.V. (bed volume) h -1 using an As(III) spiked (320 μg l -1 ) natural tap water sample from Presidency College, Kolkata. Reuse of the bed after regeneration shows a decrease in As(III) removal efficiency to the extent of 20-25% of that of a fresh column. Arsenic recovery (∼ 99.25%) from the regenerate is also reported.