Arsenic removal from copper smelter wastewater by electrocoagulation in an airlift reactor
Special Symposium - Environmental Protection & Sustainability
Environmental Protection & Sustainability (EPS - Poster)
Keywords: precipitation, coagulation, iron hydroxides, electric current, kinetic model
Copper smelters – and the sulfuric acid plants that are connected to them – generate large amount of wastewater containing heavy metals, where arsenic is the key contaminant. Heavy metals such as copper and lead can normally be removed by sulfide precipitation but arsenic needs other treatment.
Electrocoagulation to precipitate the arsenic through the in-situ production of ferric hydroxide was tested in an air lift reactor. This reactor was set up as two iron concentric cylinders. An airflow passing between the plates induced the mixing of the two phases - without the need of a stirrer -, generating turbulent conditions.
A set of synthetic wastewaters was used to test the performance of the reactor. The initial concentration varied from 100 to 5000 ppm of arsenic. Continuos current with current reversal each 120 seconds in order to avoid the passivation of the electrodes was applied. The gap between the electrodes was 10 mm for the reactor, and the current density was varied between 0.8 – 3 mA/dm2 depending on experiment. The reactor was run in continuos and batch wise operation, and the elapsed time for each experiment was 120 to 180 minutes. The results from the batch experiments were used to predict the performance of the continuos experiments and vice versa as a validation procedure.
In general the arsenic removal was efficient – e.g. a batch reactor experiment run at 1.2 mA/dm2 and initially 100 ppm arsenic showed that a more than 98 % reduction in the arsenic concentration after 3 hours was possible.
Residence time distribution experiments were run on both types of reactors, and a model that takes in account a) the kinetics on the solid phase (electrochemical phenomena), b) the mass transfer process, c) the ferrous ion oxidation with the ferric hydroxide production, and d) residence time distribution models, was developed and the kinetic parameters were fitted.
A set of residence time distribution and kinetic experiments were run on pilot scale with an airlift reactor to determine a model for the hydrodynamic and the kinetic parameters. Based on these results a scale up procedure was developed to design an actual full scale electrocoagulation reactor. The reactor is compared process wise and cost wise with the conventional industrial reactor that use ferric sulfate addition the precipitate arsenic.
Presented Monday 17, 13:30 to 15:00, in session Environmental Protection & Sustainability (EPS - Poster) S-7P.
