An Suggestion for Processing of Air pollution in Hong Kong

I am following the similar line of thinking as in the last post. It has been my dream that government build giant air cleaner to remove the pollutant from the air. However, how to maintain it financially? We could see if we could extract useful material (like heavy metal of Aluminum, Lead?) from the collected pollutant, that sell it to local/oversea industry as a supply of metallic material. This is killing two birds in one stone, we can improve the quality of the air(thereby reduce the expense in Department of Health) while making a profitable business. Thus it gives incentive for the government to clean up the air without costing taxpayer a dime. The pain would be how to implement this idea, that belong to the field of chemistries and engineers!