K. C. SEN, S. C. RAY AND S. K. TALAPATRA 269
TABLEVI
Recovery of minerals after alkali treatment
|
Silica |
Soluble |
Calcium |
Magne- |
Potas- |
Sodium |
Phos- |
Chlorine |
||
|
Wheat straw No. 1 |
Total amount |
9.74 |
8.98 |
0.37 |
0.24 |
2.08 |
0.13 |
0.17 |
0.017 |
|
Total amount |
7.87 |
4.11 |
0.50 |
0.23 |
0.46 |
0.80 |
0.08 |
nil |
|
|
Percentage re- |
80.8 |
45.8 |
135.0 |
96.0 |
22.1 |
615.4 |
47.0 |
ml |
|
|
Paddy straw No. 1 |
Total amount |
23.04 |
10.13 |
0.52 |
0.47 |
4.52 |
0.07 |
0.22 |
0.306 |
|
Total amount |
15.75 |
4.67 |
0.66 |
0.46 |
1.18 |
1.30 |
0.11 |
0.008 |
|
|
Percentage re- |
68.4 |
46.1 |
127.0 |
98.0 |
26.1 |
1,857.0 |
50.0 |
2.6 |
The data show that the mineral constituents estimated were not uniformly
affected by the treatment. Thus the percentage of potassium, phosphorus
and chlorine were significantly lowered in the treated straws. The lowered
percentage of these minerals, when considered along with the loss sustained
in dry matter, show that during alkali treatment, considerable amounts of
these minerals were washed out of the straw. On the other hand, the per-
centages of calcium, magnesium and sodium were considerably increased in
the treated straws. These minerals were not apparently affected by the
alkali treatment. The total recovery of calcium, as shown in Table VI,
moreover, suggests that, during alkali treatment of the straws, some calcium
was deposited from an extraneous source. A later examination of the tap
water showed that it contained significant amounts of calcium which were
deposited on the straw during the course of treatment. The increase in the
sodium content of treated straws was obviously due to a certain amount of
the alkali having been absorbed in spite of the repeated washings.
(c) Since, after one treatment, the alkali is only partially exhausted,
it can be used again and thereby considerable economy can be effected. Ac-
cording to Godden [1920], by bringing the strength of the residual liquor
after each treatment up to its original strength, it may be made to serve for
several batches of straw. He calculated roughly that, for every 100 lb. of
treated straw 5 lb. of soda would be used up. In the present investigation,
the strength of the alkali in the mixed solution of residual liquor and the first
wash water was determined after the treatment of wheat and paddy straw.
The results obtained were as follows :—
1. The strength and composition of alkali solution before treatment :
|
(a) amount of NaOH . . . . . |
18.90 gm. |
|
(b) amount of Na2CO3 . . . . . |
1.40 gm. |
|
Total as Na2CO . . . . . |
26.44 gm. |