Abstract: 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.sup.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.degree. C. to 1000.degree. 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.degree. C. and 1500.degree. C. The process, particularly adapted for irradiations with direct solar radiation.