Novel process of simultaneous removal of SO2 and NO2 by sodium humate solution.

A novel simultaneous flue gas desulfurization and denitrification (FGDD) process using sodium humate (HA-Na) solution was proposed. This study relates to the SO2/NO2 absorption efficiency and products of simultaneous removing SO2 and NO2 in a bubbling reactor, especially the effect of recycled water on the SO2/NO2 absorption. Under alkaline conditions, the sulfate content in S-containing compound decreases with the increase of NO2 concentration, whereas there is a contrary result under acidic conditions. Whether the absorption liquid is alkaline or acidic, the presence of NO2 improves the SO2 absorption into HA-Na solution, because NO2 may promote the oxidation of sulfite to sulfate. It seems that the presence of SO2 is unfavorable for the NO2 absorption, but the NO2 absorption efficiency can be improved with the cycle number rising due to the increasing amount of sulfite. Although all the ion concentrations of Na+,SO4(2-),SO3(2-), and NO3- have a gradual increase as the cycle number rises, the ion concentrations of SO4(2-) and Na+ are far more than that of the other ions, which results in a slight decrease of the SO2 absorption efficiency. However, the initial pH of HA-Na solution prepared by recycled water decreases from 10 to 8.1 with the cycle number increasing from 1 to 10, whereas the final pH (the pH after absorption reaction is finished) remains almost constant (3.3). The SO2 absorption efficiency is above 98% and the NO2 absorption efficiency may reach above 95% in the optimal condition in this process. The chief byproduct is a compound fertilizer consisting of humic acid (HA), sulfate, and nitrate.