Abstract: A mixing tee assembly suitable for phosphate acid attack reaction is described. The mixing tee assembly comprises an outer pipe having a mixing end and a tee end, wherein a tee structure is formed near the tee end to connect with additional piping; an inner pipe comprising a nozzle end connected to a nozzle and a open end; wherein the inner pipe is lined with a corrosion-resistant material on its inside surface; wherein when the inner pipe is assembled within the outer pipe, the nozzle extends beyond the mixing end of the outer pipe by at least ? of the inside diameter of the outer pipe.