Barium Carbonate is commercially important as a basis for the manufacture of other barium compounds. In its manufacture, BaS is 1st prepared by heating the natural sulphate barytes with Carbon. The BaS is extracted from this mass with water and the solution is treated with Sodium Carbonate to precipitate the barium. In the operation of such process it is found that the solution of barium sulphide formed contains also some calcium sulphide, originating from impurities in the barytes. The solution is treated with sodium carbonate, and the precipitated mass of calcium and barium Carbonates is filtered off.



It is found that 16.45 kg of dry precipitate are removed from each 100 kg of filtrate collected. The analysis of the precipitate is 9.9% CaCO3 and 90.1% BaCO3. The analysis of the filtrate is 6.85% Na2S, 2.25% Na2CO3 and 90.9% H2O. The sodium carbonate for precipitation was added in the form of anhydrous soda ash which contained CaCO3 as an impurity.



Calculate:

a) % Excess Na2CO3

b) Composition of sulphide solution

c) Composition of dry soda ash



BaS
CaS
+ Na2CO3 BaCO3
CaCO3
+ Na2S
anhydrous with
CaCO3 impurity
Precipitate
16.45 kg per 100 kg filtrate
9.9% CaCO3
90.1% BaCO3
filtrate
6.85% Na2S
2.25% Na2CO3
90.9% H2O




Basis: 100 kg filtrate

Since we have a basis of 100 kg filtrate we will have the following masses:

6.85 kg Na2S → formed from rxn of BaS and CaS

2.25 kg Na2CO3 → unreacted Na2CO3

90.9 kg H2O → water from Sulfide Solution

16.45 kg precipitate → combined mass of Barium and Calcium Carbonates



a) Find % excess Na2CO3:

mreacted Na2CO3 = (6.85) [Na2CO3]/[Na2S] = 11.56 kg
% excess =          unreacted         
Reacted + unreacted
x 100%
=          2.25         
11.56 + 2.25
x 100%
= 19.47%



Solving for additional masses, Let:

x = mass of Na2S formed from rxn of BaS

y = mass of CaCO3 impurity from dry soda ash



mBaCO3 = 16.45(0.901) = x [BaCO3]/[Na2S]


x = 5.86 kg



mprecipitate = mass of BaCO3 formed + mass of CaCO3 formed from rxn + mass of CaCO3 from dry soda ash

16.45 = x [BaCO3]/[Na2S] + (6.85-x) [CaCO3]/[Na2S] + y


y = 0.3580 kg



b) composition of Sulfide Solution

mBaS = 5.86 [BaS]/[Na2S] = 12.72 kg = 12.17%

mCaS = (6.85-5.86) [CaS]/[Na2S] = 0.9138 kg = 0.87%

mwater = 90.9 kg = 86.96%

mtotal Sulfide Solution = 104. 5338 kg



c) composition of dry soda ash

mass Na2CO3 = 11.56 kg = 97%

mass CaCO3 = 0.3580 kg = 3%

mass total dry soda ash = 11.918 kg


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