(539c) Removal of Arsenic in Water With An Adsorbent Derived From Waste Concrete Sludge

Introduction:

Novel adsorbents for removal of arsenic in waster were prepared from concrete wastes including waste cement powder and concrete sludge. The waste cement powder is fine particle of which the main component is hydrated cement, which is generated as waste in the recycling process of aggregates from waste concrete. The concrete sludge is waste of raw concrete generated and disposed of from construction sites.

Experimental:

(1) Adsorbent from waste cement. The waste cement particle supplied from a waste concrete recycling plant was used as an adsorbent for the arsenic removal experiment after sieving. The diamter range was 53 to 106 μm.

(2) Adsorbent from concrete sludge. The concrete sludge, which is generated in a concrete product plant, is first diluted with water; this pretreatment could avoid the hardening reaction of concrete. Then solid was separated from aqueous phase, and dried under various temperatures. The dried solid was then pulverized and thieved. The adsorbent so prepared with the diameter range of 53 to 106 μm was used for the arsenic removal experiment.

The arsenic removal experiment was conducted in a batch reactor with stirring under room temperature. The concentration (As (V)) of the solution was changed in the range of 10 to 700 mg-As/L. The ratio of solution to the adsorbent was changed in the range of 67 to 400. The stirring rate was fixed at 350 rpm, which is considered to be high enough to neglect the mass transfer resistance in the aqueous phase. The solution was sampled with filtration, and the concentration change was measured with ICP-AES.

Results and discussion:

It was confirmed that the arsenic concentration decreased with time for all the adsorbents studied. When adsorbent derived from concrete sludge was used, the final concentration of arsenic after 24 h for the initial concentration at 100 mg/L was lower than 0.1 mg/L, which is below the effluent standard for the waste water in Japan. In addition, the removal rate was much higher with the adsorbents from concrete sludge than those from waste cement. The capacity of the arsenic removal with the adsorbent prepared from concrete sludge was about 170 mg-As/g-adsorbent based on the removal experiments of various initial concentrations. This capacity is comparable with the ones of the conventional adsorbents. The arsenic was removed mainly in the form of calcium salts according to XRD analysis of the solid phase after removal.  By considering the preparation cost, which is derived from waste, the present adsorbents could be widely applicable to the water treatment, especially in developing countries.