I 
MANUFACTURE OF PHOSPHORIC ACID. 
31 
In several cases it will be noted that the quantity of phosphoric 
acid in the briquet ted charge is from 1 to 1.5 per cent below that in 
other mixtures. This is due chiefly to the fact that in addition to the 
lime combined with phosphoric acid a part of this base present in the 
original phosphate samples was in the form of carbonate and there- 
fore the sand added to take care of the lime in this latter compound 
reduced the percentage of phosphoric acid in the briquets. 
In preparing the samples for briquetting purposes it was found 
that a Sturtevant hammer mill w^ould grind run-of-mine phosphate, 
containing as high as 10 per cent of moisture, to 15 mesh without 
clogging the mill. From a commercial standpoint this is a very im- 
portant item, since much of the material as it comes from the mines 
contains a high percentage of moisture, the removal of which would 
prove quite costly. Moreover, since the presence of from 7 to 10 per 
cent of moisture in the final mixture is necessary in order to give the 
material the proper plastic qualities for briquetting purposes, it would 
be unfortunate to have to dry the phosphate only to wet it again in 
order to briquet it. Where the material is so dry that it requires the 
addition of moisture before it can be briquetted, the water can best 
be added to the sand and coke, with which the phosphate is subse- 
quently mixed. It has been found unnecessary to grind the phos- 
phate finer than that which will go through a sieve having 15 meshes 
to the linear inch, although finer grinding aids somewhat in impart- 
ing greater resisting power to the briquets and probably accelerates 
slightly the rate of the reactions in the furnace. 
The briquetting machine of semicommercial size used in preparing 
the phosphate charges for furnace treatment is illustrated in Plate II. 
In Tables 16' and 17 are given the results of the shatter and com- 
pression tests on briquets made from mixtures of relatively high-grade 
phosphate, sand, and coke, as well as those on briquets made up of 
mixtures of two or more phosphates. The briquets were made up 
with varying percentages of moisture and the shatter and compres- 
sion tests were applied not only to the freshly made briquets but also 
to the air-dried and oven-dried samples. 
Table 16. — Shatter tests on briquets made from natural phosphate rock, sand, and cokt. 
Sample Xo. 
1-F . 
1-F . 
1-F . 
2.... 
3-T . 
3-T . 
3-T . 
o-T . 
5-T . 
7-T . 
7-T . 
7-T . 
14-T 
14-T 
15-T 
15-T 
15-T 
18-T 
Fresh briquets. 
(Shattered 
on 
Weights. H 2 0. ! dr °PP in K 
! cement 
floor. 
Grams- 
107.0 
105.5 
108.7 
110.0 
133.5 
124.7 
115.2 
113.7 
126.4 
122.1 
103. 2 
116.4 
131.3 
120-9 
121.7 
119.2 
115.7 
120.6 
r cent. 
Feet. 
11.21 
5 
13.53 
10 
13. 45 
20+ 
10.00 
20+ 
8.69 
4 
11.15 
8 
13. 63 
14 
11.08 
8 
13.13 
12 
10.49 
9.50 
8 
13.14 
10 
9.90 
9 
10.47 
12 
9.53 
6 
12.35 
20 
12.62 
12 
13.27 
20+ 
Air-driei briquets. 
Shattered! With- 
on J stood 
dropping i drop on 
to 
cement 
floor. 
Feet- 
mass of 
similar 
briquets. 
Feet. 
Compres- 
sion 
test. 
Pounds 
per sq. in. 
472 
800 
83S 
483 
654 
15 
16 
18 
18 ! 
20 
20 
20 
20 , 
815 
950 
724 
793 
407 
894 
53 s 
887 
Oven-dried 
briquets. 
Shattered 
on 
dropping 
to 
cement 
floor. 
Feet. 
With- 
stood 
drop on 
mass of 
similar 
briquets. 
Feet. 
'Average weight=109 grams. Average H 2 content=2.95 per cent. 
