One of the by-products formed during the recovery of NH$$_3$$ from Solvay process is:

In the Solvay process, ammonia is recovered by treating the ammonium chloride ($$\text{NH}_4\text{Cl}$$) by-product with calcium hydroxide ($$\text{Ca(OH)}_2$$, obtained from slaking quicklime). The reaction is: $$2\text{NH}_4\text{Cl} + \text{Ca(OH)}_2 \to 2\text{NH}_3 + \text{CaCl}_2 + 2\text{H}_2\text{O}$$.

From this reaction, when ammonia is recovered, calcium chloride ($$\text{CaCl}_2$$) is formed as a by-product. Therefore, one of the by-products formed during the recovery of $$\text{NH}_3$$ from the Solvay process is $$\text{CaCl}_2$$.