Multi-Pollutant Gas Purification Process with Alkali Sorbent and De-NOx supported catalyst comprising Ca-deficient hydroxyapatite

Process for treating a combustion waste gas stream containing NOx and contaminants such as heavy metals and/or acid gases, e.g., halogens, SOx, comprising: injecting an alkali sorbent, into the waste gas stream; removing some contaminants with the alkali sorbent from the waste gas stream; injecting an ammonia source into the gas stream; injecting a deNOx catalyst into the gas stream at a temperature of 100°C to preferably not more than 600°C to reduce with NH3, in the presence of O2, some NOx to N2 and water in the gas stream, wherein the deNOx catalyst comprises copper and/or copper oxide deposited on a porous support comprising at least 60 wt % of a calcium-deficient hydroxyapatite having a Ca/P of less than 1.67. A blend comprising the alkali sorbent and the deNOx catalyst may be formed to inject them together into the waste gas stream. The ammonia source and the deNOx catalyst are preferably injected simultaneously. Alternatively, the ammonia source may be included in the alkali sorbent and/or the deNOx catalyst.