NOVELTY - The method comprises contacting (420) a flue gas from a natural gas-burning power plant with an aqueous composition comprising a proton-removing agent by an electrochemical process under conditions to produce a deprotonated carbonate, producing (430) a carbonate-containing precipitation material from the deprotonated carbonate, electrochemically producing the proton-removing agent, and processing the carbonate-containing precipitation material to produce a building material consisting of hydraulic cement, a supplementary cementitious material, and/or aggregate.    USE - The method is useful for sequestering carbon dioxide from a multi-component gaseous stream such as flue gas from natural-gas burning power plant.    ADVANTAGE - The method is capable of economically and safely sequestering the carbon dioxide from the multi-component gaseous stream with reduced energy consumption and less parasitic load and without potential risks of climate change.    DETAILED DESCRIPTION - The method comprises contacting (420) a flue gas from a natural gas-burning power plant with an aqueous composition comprising a proton-removing agent by an electrochemical process under conditions to produce a deprotonated carbonate, producing (430) a carbonate-containing precipitation material from the deprotonated carbonate, electrochemically producing the proton-removing agent, and processing the carbonate-containing precipitation material to produce a building material consisting of hydraulic cement, a supplementary cementitious material, and/or aggregate. The natural gas-burning power plant generates 0.1-1 ton of carbon dioxide per megawatt hour. The electrochemical process: consumes less than or equal to 70 energy than an amount of energy generated during production of the flue gas from the natural gas-burning power plant; runs at a voltage of less than or equal to 1.2 V; and comprises contacting an anode with a first electrolyte, contacting a cathode with a second electrolyte, disposing an ion exchange membrane between the anode and the cathode, producing hydroxide ions in the second electrolyte without forming an oxygen or chlorine gas at the anode, and forming hydrogen ions using hydrogen gas at the anode. An INDEPENDENT CLAIM is included for a system for sequestering carbon dioxide from a multi-component gaseous stream.    DESCRIPTION OF DRAWING(S) - The diagram shows flow chart of a method for separating carbon dioxide from a multi-component gaseous stream.    Contacting aqueous composition source with multi-component gaseous stream (410)    Contacting carbon dioxide containing multi-component gaseous stream with aqueous composition (420)    Producing protonated carbonate composition (430)    Removing proton from the protonated carbonate composition (435)    Sequestering produced protonated carbonate composition. (440)