a process for recycling waste sulfuric acid by decomposing organic contaminants by use of light energy , comprising exposing a waste sulfuric acid containing contaminants to a focused radiation emission having an irradiation intensity within the range of from 0 . 01 to 100 mw / m 2 in a reaction chamber shaped as a directly - absorbing receiver , wherein the chamber is maintained at a temperature within the range of from 200 ° c . to 1000 ° c . to form sulfur trioxide and water as sulfuric acid decomposition products . the process also includes forming sulfur dioxide and oxygen , starting materials for sulfuric acid , by cleavage of the decomposition product sulfur trioxide by maintaining the reaction chamber at a temperature between 400 ° c . and 1500 ° c . the process , particularly adapted for irradiations with direct solar radiation .