Removal of arsenic from simulated groundwater using calcined laterite as the adsorbent

Arsenic, which is well known as a carcinogen, occurs naturally in the earth’s crust such as in rocks, soil, and water. Unfortunately, it easily penetrates into groundwater from soil and waste water. The presence of arsenic in groundwater has been reported to cause cancer of the lungs, kidney, liver and skin due to chronic arsenic poisoning. Laterite (limonite), which is available in Palawan, Philippines, was used as an adsorbent for the removal of arsenic from simulated groundwater. The adsorbent characteristics, which were investigated using BET, SEM/EDX, XRD/XRF, showed that calcined laterite is a porous adsorbent with a surface area of 87.5m2 /g, high iron content (71.9 %w.t); and the iron present in mineral phase of calcined laterite is hematite (Fe2O3). Calcined laterite could remove 99.42% total arsenic after 24h treatment with 0.81mg/L initial arsenic concentration and 5g/L of adsorbent dosage. Batch experiments were carried out by varying the initial arsenic concentrations in the range of 0.361-5.073mg/L conducted at 33o C. Isotherm results indicated that arsenic adsorption can be described well by both Langmuir model and Freundlich model. The maximum adsorption capacity obtained from Langmuir model is 5.058mgAs/g calcined laterite, and the Freundlich adsorption capacity (KF) is 0.161L/g. A column (2.5mm I.D; 55cm height) was used to investigate the arsenic removal on a continuous up-flow fixed bed column. The results showed that an increase in the flow rate from 5 to 15mL/min decreased the breakthrough time from 684 to 192h. A decrease in the inlet arsenic concentration from 1.657mg/L to 0.462mg/L resulted to an increase in breakthrough time from 78 to 325h. Breakthrough occurred late at higher bed depths. Breakthrough time at highest bed depth of 30cm was 490h. The highest treated volume was 205.2L at 5mL/min flow rate while the highest treated volume was 292.5L at 0.462mg/L inlet arsenic concentration. The Thomas Model described well the breakthrough curve and predicted adsorption capacity for different flow rates and inlet arsenic concentrations. The Bed Depth Service Time (BDST) Model agreed well the experiment values with the breakthrough time at different bed height. The treated water before breakthrough time could meet the WHO guideline of maximum arsenic contamination in drinking water which is 0.01mg/L