1918.] 
The N.Z. Journal of Science and Technology. 
317 
air-current, and the speed adjusted to allow complete roasting, which takes 
from ten to thirty-six minutes. On the down and return journey the stuff 
is dumped on to screens. 
These three roasting processes are very suitable for both ore and flue- 
dust (if not too carbonaceous), and give relatively low cost for initial 
outlay and working-expenses. The cost per ton varies from Is. 6d. to 4s. 
in America, and the processes are making great headway in recent years. 
Desulphurization is very active and complete, and even pyrites can be 
handled, but, of course, coal free from sulphur must be used. In each 
process the ore must be tempered with water. 
Conclusion .—Briquettes made by pressure alone are seldom satisfactory. 
The Grondal process has special advantages under Swedish conditions 
(where low furnaces are used which burn charcoal), but seems too expensive 
elsewhere. The true briquetting processes all involve separate handling 
of each brick, entailing heavy cost and much breakage. Even the 
Schumacker process, which avails itself of the existing hydraulic properties 
of flue-dust, has been superseded by a roasting process at the Gelsenkirchener 
works. The rotary-kiln process is still the most largely used, but the 
roasting processes are making rapid headway and give a satisfactory 
briquette, hard, strong, and sufficiently porous. 
In conclusion, ore-briquetting or sintering is far from being a simple 
operation, and every material or ore requires experimental treatment before 
expensive plant is erected on experience elsewhere. The cost is greatly 
affected by local conditions of freight, labour, facilities of plant, &c., and 
particularly liberal allowances for the optimism of inventors seem rendered 
necessary by past experience. 
Abstractor’s Note. 
The briquetting of iron-ores and flue-dust has been practised for many 
years with varying success ; but modern mining with high explosives, 
modern bulk methods of transporting ore, and modern high-pressure blast 
have increased the percentage of fine ore and flue-dust available, and made 
the question one of great importance. New Zealand is vitally interested 
in the problem because briquetting offers the most obvious method of 
attacking Taranaki ironsand. It is noteworthy that a very early proposal 
for the briquetting of ores was made before the Wellington Philosophical 
Society, in 1868, bv R. Pharazyn.* 
New-Zealanders are apt to look on Taranaki sand as a unique ore of 
iron, but large deposits of similar sand exist in other places (St. Lawrence 
River, California, Naples, &c.), and long years of experimenting have failed 
to bring a satisfactory solution of the briquetting problem. The only 
case in which briquettes are used as the sole burden of the blast 
furnace occurs in the low charcoal furnace of Sweden ; in America a burden 
of 25 per cent, briquettes is looked on as very good practice. It may 
fairly be stated that no process of briquetting with fancy binding- 
mediums will be successful, and sole reliance must be placed on the 
formation of the sticky ferric hydroxide. If Taranaki sand is ever success¬ 
fully treated in a commercial blast furnace (and the prospect is not hopeful) 
it will probablv be after preliminary nodulizing in a kiln or pot process. 
S. H. J. 
* R. Pharazyn, Suggestions and Experiments on the Smelting of Taranaki Iron- 
sands, Trans. N.Z. Inst., vol. 1, 2nd ed., p. 437. 
