preferred embodiment a ported rotary kiln would be utilized in such a kiln the feed material or pelletized ore is placed within a ported type rotary kiln such kilns are well known and appreciated by those skilled in the art and are described in u s pat nos 3 182 980 3 847 538 3 945 824 and 4 070 149 the disclosures of these four patents are expressly incorporated herein by reference ported rotary kilns achieve uniform or near uniform temperature distribution by means of multiple spaced apart ports in the kiln walls which allows fuel and air to be fired evenly over and across the length of the kiln bed it should be noted that uniform temperature distribution is desirable because in cases where there is a non uniform temperature distribution along the length of a kiln may result in fusing or melting of the ore pellets however the ported kiln may be used with a single gas burner located at one end of the kiln in both configurations inert gas is fed through the ports under the phosphate ore bed as a third alternative the process can be operated using a kiln that does not have ports and which is fitted with a single gas burner as noted.