Process for treating a nox containing gas

A process for treating a NOx-containing gas resulting from a leaching process wherein said leaching process includes the treatment of ores with nitric acid to separate materials contained in the ores, and said leaching process releases a diluted nitric acid solution and said NOx-containing gas, the process comprising:

• ai) an absorption step in presence of make-up water and/or in presence of diluted nitric acid, obtaining a concentrated nitric acid and a tail gas containing residual NOx;
• a) a compression step wherein said NOx-containing gas is subjected to compression to yield a pressure-adjusted gas;
• b) a first heat transfer step wherein heat is removed from said pressure adjusted gas to yield a temperature adjusted gas;
• c) a condensation step wherein said temperature adjusted gas is subject to condensation to yield a condensate stream and a nitrous gas;
• d) an absorption step wherein said condensate stream and said nitrous gas is subjected to an absorption step in presence of make-up water and/or diluted nitric acid to yield said concentrated nitric acid and said tail gas containing residual NOx;
• e) a second heat transfer step wherein said tail gas is heated to yield a heated tail gas;
• f) an expansion step wherein said heated tail gas is expanded to recover power;
• wherein said nitrous gas of step c), before being supplied to said absorption step, is further subjected in sequence to a high-pressure compression, a heat recovery, a condensation step, wherein said high-pressure compression is carried out at a pressure higher than said compression of step a).

A process for treating a NOx containing gas, wherein said NOx containing gas includes NO, NO2 and N2O4 and wherein the sum of NO, NO2 and N2O4 in said NOx containing gas is comprised between 3% and 60% mol, preferably between 5% and 20% mol;

• the process comprising:
• a) subjecting said NOx containing gas to a compression step to yield a pressure-adjusted gas;
• b) subjecting said pressure-adjusted gas to a first heat recovery step to yield a temperature adjusted gas;
• c) subjecting said temperature adjusted gas to a condensation step to yield a condensate stream and a nitrous gas;
• d) subjecting said condensate stream and said nitrous gas to an absorption step in presence of make-up water and/or diluted nitric acid to yield a concentrated nitric acid and a tail gas containing residual NOx;
• e) adjusting the temperature of said tail gas containing residual NOx by transferring heat from said pressure adjusted gas of step c) to said tail gas containing residual NOx to yield a heated tail gas;
• f) subjecting said heated gas to an expansion step to recover power to be used in said compression step.

A gas treatment section configured to treat a NOx-containing gas from a leaching section, wherein:

• in the leaching section, ores are contacted with a nitric acid to generate a diluted nitric acid solution containing target elements separated from said ores, and a NOx containing gas is produced;
• the gas treatment section comprising:
• an absorption unit in fluid communication with said leaching section and configured to contact a NOx containing gas with a make-up water and/or diluted nitric acid to generate a concentrate nitric acid;
• a low-pressure nitric acid recovery section comprising:
• a low-pressure compressor and a low-pressure expander connected in series wherein said low-pressure compressor has an input that is fluid communication with said leaching section;
• a low-pressure heat recovery section including a heat exchanger and a low-pressure condenser, said low-pressure heat recovery section is in fluid communication with an outlet of said low-pressure compressor and with an inlet of said absorption unit;
• a line connecting said absorption unit with said low-pressure expander;
• a driver connected with said low-pressure compressor section and with said low-pressure expander section and arranged to transmit power to said low-pressure compressor section;
• a high-pressure nitric acid recovery section in communication with said low-pressure heat recovery section and with said absorption unit, wherein said high-pressure nitric acid recovery section includes:
• a high-pressure compressor and a high-pressure expander connected in series wherein said high-pressure compressor has an input that is in fluid communication with said low-pressure heat recovery section;
• a high-pressure heat recovery section including a heat exchanger and a high-pressure condenser wherein said heat exchanger is in fluid communication with an outlet of said high-pressure compressor;
• a line connecting said high-pressure heat recovery section with said absorption section.