about 15 000 ppm ti 4 ions can be contacted with an aqueous alkaline precipitant solution to form a reactant mixture comprising a precipitate the initial titanium ion concentration iron concentration and sulfuric acid concentration of the waste sulfuric acid to be treated can vary as described herein in connection with the acid precipitation method any suitable alkaline precipitant solution can be used for example the aqueous alkaline precipitant solution can comprise an aqueous sodium phosphate solution for example a sodium hexa meta phosphate solution the aqueous alkaline precipitant solution can comprise for example from about 5 0 by weight sodium hexa meta phosphate to about 50 by weight sodium hexa meta phosphate from about 10 by weight sodium hexa meta phosphate to about 20 by weight sodium hexa meta phosphate or from about 14 by weight sodium hexa meta phosphate to about 16 by weight sodium hexa meta phosphate based on the total volume of the waste sulfuric acid solution the reactant mixture can be heated to a temperature of from 50 u00b0 c to 200 u00b0 c for example at a temperature of from about 75 u00b0 c to about 150 u00b0 c to form a digest mixture comprising a supernatant and a precipitate heating temperatures and durations can vary as described herein in connection with the acid precipitation method in some embodiments the contacting causes an exothermic reaction and heating the digest mixture can result from the contact with the alkaline precipitant such that no heater is needed or used for heating the reactant mixture the supernatant.