Recovering chemicals from wastewater occurring during production of lignocellulosic fibers, comprises guiding the wastewater between the ion-selective walls and then flowing-through by electric current, where the walls are bipolar walls

摘要

The method for recovering chemicals from wastewater (1) occurring during the production of lignocellulosic fibers, comprises guiding the wastewater between the ion-selective walls (3, 3') and then flowing-through by electric current, where a flow of received ions to the wastewater and a flow of ions delivered from the wastewater are produced through the ion-selective walls. The walls are permeable only for cations and anions. The cation-permeable or anion-permeable walls alternate transverse to the flow direction of the wastewater, where the walls are bipolar walls. The method for recovering chemicals from wastewater (1) occurring during the production of lignocellulosic fibers, comprises guiding the wastewater between the ion-selective walls (3, 3') and then flowing-through by electric current, where a flow of received ions to the wastewater and a flow of ions delivered from the wastewater are produced through the ion-selective walls. The walls are permeable only for cations and anions. The cation-permeable or anion-permeable walls alternate transverse to the flow direction of the wastewater, where the walls are bipolar walls. The cation-permeable walls and bipolar walls alternate transverse to the flow direction of the wastewater. The anion-permeable and bipolar walls alternate transverse to the flow direction of the wastewater. The wastewater contains lignosulfate based on sodium, magnesium, calcium or ammonium. The flow of the ions received from the wastewater consists of positive hydrogen ions and the flow of ions delivered from the wastewater consists of positive sodium-, magnesium-, calcium- or ammonium ions, where lignin sulfonic acid is formed in the wastewater. A receiving solution, which contains sulfuric acid or its salts, is guided into a reaction chamber (6) with the walls partially permeable for ions and is flowed-through by the electric current. The inflow of sodium ions in the receiving solution and flow of the hydrogen ions from the receiving solution to the wastewater guided into an adjacent reaction chamber are produced through the walls. An electrochemical rinsing liquid is guided into the reaction chamber with sodium sulfate containing cations delivered from the wastewater. The further reaction chamber has hydrogen ions forming anode (14) and walls partially permeable for ions. The rinsing liquid is flowed-through by the electric current. The flow of the sodium ions delivered from the wastewater to the receiving solution guided into the adjacent reaction chamber is produced through the walls. The sodium sulfate is converted into sodium hydrogen sulfate through the inflow of the protons and the outflow of the sodium ions. The hydrogen sulfate is fed into a further electrochemical rinsing solution of a further reaction chamber, which has a hydroxide-ion forming cathode (15) and a wall partially permeable for ions. The flow of the sodium ions delivered from the wastewater to the further rinsing solution guided into the reaction chamber is produced through the walls. The sodium hydrogen sulfate is converted into sodium sulfate containing cations delivered from the wastewater through the inflow of the sodium ions and hydrogen ions delivered from the wastewater.