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:

m_reacted 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



m_BaCO3 = 16.45(0.901) = x [BaCO₃]/[Na₂S]


x = 5.86 kg



m_precipitate = 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

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

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

m_water = 90.9 kg = 86.96%

m_total 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