Method for treating hexavalent chromium-containing aqueous solution

A method for treating a hexavalent chromium-containing aqueous solution, comprising:

• a step (a) of adding catalyst particles to the aqueous solution;
• a step (b) of reducing hexavalent chromium by irradiating the aqueous solution with ultraviolet light having a wavelength in a range between 200 nanometers and 400 nanometers, both inclusive, while stirring the catalyst particles in the aqueous solution;
• and
• a step (c) of stopping the stirring in the step (b) and separating the catalyst particles from the aqueous solution by sedimentation,
• wherein each catalyst particle is composed only of a titanium dioxide particle having an average particle diameter in the range of 1 nm to 100 nm and a zeolite particle having a particle diameter of 1 μm to 10 μm, the titanium dioxide particle is adsorbed on an outer surface of the zeolite particle, the zeolite particle includes silica and alumina, and the catalyst particles are contained in the aqueous solution at a concentration in a range between 0.4 grams/liter and 16 grams/liter, both inclusive, and
• a change in laser light transmittance of the aqueous solution from before sedimentation to after a sedimentation duration of 30 minutes in the step (c) is 20% or more.