Strontium carbonate can be calcined in a rotary kiln without excessive liquid formation if it is admixed with at least 8 percent finely divided carbon and the kiln is operated with not less than 2 percent combustibles in the exit gases when at least 85 percent of the strontium carbonate feed passes a 325 mesh screen. Under these conditions, the mixture of strontium carbonate and carbon forms agglomerates soon after entering the kiln, minimizing premature burning of the carbon and preventing sticking of the strontium carbonate to the kiln wall.