Method for reducing perfluorocarbon emissions from aluminum electrolysis

Abstract

The disclosure provides a method for reducing perfluorocarbon emissions from an aluminum electrolysis, which belongs to the field of aluminum electrolysis. The method includes: placing an aluminum oxide in an electrolytic cell with set parameters for proceeding aluminum electrolysis, and regulating feeding parameters of the aluminum oxide to obtain an electrolyte; adding a set amount of LiF, KF, MgF 2 and CaF 2 into the electrolyte, and regulating a molar ratio of NaF and AlF 3 in the electrolyte to reduce the perfluorocarbon emissions from the aluminum electrolysis.

What is claimed is: 
     
         1 . A method for reducing emissions of perfluorocarbons from an aluminum electrolysis, comprising:
 placing an aluminum oxide in an electrolytic cell with set parameters for proceeding the aluminum electrolysis, and regulating feeding parameters of the aluminum oxide to obtain an electrolyte; and   adding a set amount of LiF, KF, MgF 2  and CaF 2  into the electrolyte and regulating a molar ratio of NaF and AlF 3  in the electrolyte to reduce the perfluorocarbon emissions from the aluminum electrolysis.   
     
     
         2 . The method for reducing the perfluorocarbon emissions from the aluminum electrolysis according to  claim 1 , wherein the adding a set amount of LiF, KF, MgF 2  and CaF 2  into the electrolyte and regulating a molar ratio of NaF and AlF 3  in the electrolyte satisfies the following relation formula:
 CR=3.334−0.0446×w(KF) eletrolyte +0.0942×w(LiF) eletrolyte +0.0098×w(MgF 2 ) electrolyte −0.0070×ΔT−0.0895×AO−0.0452×t+r where CR represents a molar ratio of NaF and AlF 3 ; w(KF) electrolyte , w(LiF) electrolyte  and w(MgF 2 ) eletrolyte  represent mass fractions of KF, LiF, and MgF 2  in the electrolyte respectively; ΔT represents a superheat degree of the electrolyte, a unit of ΔT being ° C.; AO represents a type of the aluminum oxide, wherein when the aluminum oxide is a flour aluminum oxide, AO=1, and when the aluminum oxide is an intermediate aluminum oxide, AO=2, and when the aluminum oxide is a sandy aluminum oxide, AO=3; t represents a time for 1% aluminum oxide to be completely dissolved in a molten electrolyte, and t≤20, a unit of t being min; and r represents an adjustment constant, and r=0−0.1.   
     
     
         3 . The method for reducing the perfluorocarbon emissions from the aluminum electrolysis according to  claim 1 , wherein the set parameters comprise at least one selected from the group consisting of:
 an average superheat degree being 8−15° C. and an electrolyte height≥19 cm.   
     
     
         4 . The method for reducing the perfluorocarbon emissions from the aluminum electrolysis according to  claim 1 , wherein the feeding parameters comprise at least one selected from the group consisting of:
 a break through rate of a feeding hole≥90%, a coverage rate of the feeding hole by carbon residue≤80%, a deviation of a feeding amount of the aluminum oxide from a theoretical value≤10%, and a lowest concentration of the aluminum oxide≥1.2%.