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⁺,SO₄²⁻,SO₃²⁻, and NO₃⁻ have a gradual increase as the cycle number rises, the ion concentrations of SO₄²⁻ 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.