Useful Phosphate Rock

Press, Volume CV, Issue 30965, 22 January 1966, Page 9

Useful Phosphate Rock

Christmas Island, in the Indian Ocean, is expected to yield large amounts of a type of phosphate rock which is proving very promising as a fertiliser in trials in various parts of New Zealand. Development of these resources is expected to be of considerable economic sig-

niflcance to New Zealand because of the country’s dependence on phosphate and because sources of higher grade material are dwindling on Nauru and Ocean Islands, in the Pacific.

The new material, which is classified as lower grade in its untreated state, is not suitable for superphosphate manufacture with the addition of sulphur. But after intense heat treatment it yields more phosphate than super and is likely

to be considerably cheaper. Dr. B. W. Doak, senior fertiliser research officer to the British Phosphate Commission in Melbourne, said in Auckland recently that very high hopes were held for this calcined material. It was possible that production would begin in 1968. Formerly director of the New Zealand fertiliser industry research station at Otara, near Auckland, Dr. Doak took up a special appointment with the British Phosphate Commission in Australia about 15 months ago. Dr. Doak has been particularly concerned with the investigation of phosphate deposits on Christmas Island. He had been in New Zealand inspecting trials with the new fertiliser on pastures and forests.

Before his departure for Australia Dr. Doak said that Christmas Island supplied phosphate exclusively for New Zealand and Australia, and a big expansion in phosphate mining was planned for the island.

Geological surveys now being done indicated that reserves were higher than had previously been believed. These included deposits of material which lay on top of the higher grade phosphate and which was not suitable for superphosphate manufacture. This material had to be shifted and stockpiled, said Dr. Doak. It was known that there was at least 50m tons of it, and it had been found that heat treatment greatly improved its solubility. A number of trials had been laid down in New Zealand and Australia to obtain an assessment of the material and good responses were being obtained in some areas, particularly in locations with higher rainfall. Dr. Doak said trials at Otara and at Rukuhia, near Hamilton, indicated that a 50-50 mixture of superphosphate and calcined phosphate applied at the rate of 2jcwt to the acre gave an equivalent response to 3cwt of straight superphosphate. “However,” he said, “We don’t know yet whether we will get the same sort of response in all localities. Calcined phosphate is more slowly available to the plant than superphosphate.” It was proposed to do the heat treatment on Christmas Island because the lower grade material had to be dried out in any case and because the process lightened the material and would thus save freight costs.