Process for heavy metal removal from iron- and steelmaking flue dust

Abstract

A process, for the selective heavy metal removal from iron- and/or steelmaking flue dust, including steps of: preparing a feedstock (FS) by blending or mixing a chloride precursor material (CPM) and ironmaking and/or steelmaking flue dust including heavy metals (ISFD), the heavy metals including Pb and Zn and optionally Cd; in a first reaction step in a first reactor reacting the CPM with the ISFD by thermal treatment of the FS at a temperature in a range of 700° C. to 950° C. removing at least 70 wt. % of Pb from the ISFD; in a subsequent second reaction step in a second reactor further reacting the CPM with the ISFD by thermal treatment of the feedstock FS at a temperature in a range of 850° C. to 1200° C.; and obtaining a solid material after the second reaction step. The invention also relates to a plant implementing the process.

1 . A process for the selective heavy metal removal from iron- and/or steelmaking flue dust (ISFD), the process comprising the steps of:
 preparing a feedstock (FS) by blending or mixing a chloride precursor material (CPM) and ironmaking and/or steelmaking flue dust comprising heavy metals (ISFD), the heavy metals being at least Pb and Zn and optionally also Cd;   in a first reaction step in a first reactor reacting the CPM with the ISFD by thermal treatment of the FS at a temperature in a range of 700° C. to 950° C. removing at least 70 wt. % of Pb from the ISFD by chlorination and evaporation of the Pb and removing it from the first reactor via the off-gas formed;   in a subsequent second reaction step in a second reactor further reacting the CPM with the ISFD by thermal treatment of the feedstock FS at a temperature in a range of 850° C. to 1200° C. removing the Zn from the ISFD by chlorination and evaporation of the Zn and removing it from the second reactor via the off-gas formed; and   obtaining and removing a secondary solid material after the second reaction step from the second reactor.   
     
     
         2 . The process according to  claim 1 , wherein during the first reaction step at least 70% of the Pb is removed from the ISFD by evaporating PbCl 2  at temperatures from 700° C. to 950° C. 
     
     
         3 . The process according to  claim 1 , wherein during the first reaction step at least 80 wt. % of the Pb is removed from the ISFD. 
     
     
         4 . The process according to  claim 1 , wherein during the second reaction step the zinc is removed from the ISFD by evaporating ZnCl 2  at temperatures from 850° C. to 1200° C., under a non-oxidizing atmosphere. 
     
     
         5 . The process according to  claim 1 , wherein off-gasses generated in the first reaction step in the first reactor are treated in an off-gas treatment system to obtain lead-enriched flue dust. 
     
     
         6 . The process according to  claim 1 , wherein off-gasses generated in the second reaction step in the second reactor are treated in an off-gas treatment system to obtain zinc-enriched flue dust. 
     
     
         7 . The process according to  claim 1 , wherein the ratio of ironmaking and/or steelmaking flue dust comprising ISFD and CPM being chosen so that the chloride content of the FS is between 100% and 150%, preferably between 100% and 130%, of the amount necessary for a stoichiometric conversion of the heavy metals in the ISFD into chlorides. 
     
     
         8 . The process according to  claim 1 , wherein the chloride precursor material (CPM) is selected from the group comprising consisting of polyvinyl chloride (PVC), waste comprising PVC, chlorinated rubber or other chlorinated polymers, FeCl 2 , FeCl 3 , and CaCl 2 ). 
     
     
         9 . The process according to  claim 1 , wherein the chloride precursor material (CPM) is FeCl 2 . 
     
     
         10 . The process according to  claim 1 , wherein each of the first reaction step and the second reaction step are performed in a rotary kiln. 
     
     
         11 . A method of use of the obtained secondary solid material after the second reaction step according to  claim 1 , comprising feeding the obtained secondary solid material to an ironmaking operation as a ferrous raw materials and/or carbon resource. 
     
     
         12 . A method of use of the zinc-enriched flue dust from the second reaction in the second reactor according to  claim 6 , comprising feeding the zinc-enriched flue dust to a hydrometallurgical process or electrolytic process to recover the zinc metal or zinc compounds. 
     
     
         13 . A plant for implementing the process for the selective heavy metal removal from iron- and/or steelmaking flue dust according to  claim 1 , the plant comprising
 an apparatus for preparing a feedstock FS by blending or mixing the CPM and ISFD;   a first reactor configured for the first reaction step and the first reactor being equipped with an off-gas treatment system; and   a second reactor configured for the second reaction step and the second reactor being equipped with an off-gas treatment system.   
     
     
         14 . The plant according to  claim 13 , wherein the first reactor and the second reactor are positioned in-line. 
     
     
         15 . The plant according to  claim 13 , comprising
 at least one operation selected from the group comprising a blast furnace operation, a direct reduced iron making operation, a reducing electrical furnace operation, an electric arc furnace operation, a HIsarna-type ironmaking process, and a basic oxygen steelmaking operation;   the operation(s) including off-gas generation and being equipped with an off-gas treatment system to capture the flue dust comprising heavy metals, the heavy metals being at least lead, zinc and optionally also cadmium (ISFD);   the apparatus, the first reactor and the second reactor;   the ISFD being blended or mixed in apparatus with a chloride precursor material (CPM) to prepare a feedstock (FD);   subjecting said feedstock (FD) to a thermal treatment in the first reaction step in the first reactor, and the subsequent second reaction step in the second reactor; and   the obtained secondary solid material after the second reaction step and removed from the second reactor is re-used in an ironmaking operation as ferrous containing raw material via direct injection or after agglomeration.   
     
     
         16 . The process according to  claim 1 , wherein during the first reaction step at least 70% of the Pb is removed from the ISFD by evaporating PbCl 2  at temperatures from 800° C. to 900° C., under a non-oxidizing atmosphere. 
     
     
         17 . The process according to  claim 1 , wherein during the first reaction step at least 90 wt. % of the Pb is removed from the ISFD. 
     
     
         18 . The process according to  claim 1 , wherein during the second reaction step the zinc is removed from the ISFD by evaporating ZnCl 2  at temperatures from 900° C. to 1100° C., under a non-oxidizing atmosphere. 
     
     
         19 . The plant according to  claim 13 , wherein the first reactor and the second reactor are positioned in-line, and each of the first reactor and the second reactor are a rotary kiln.