Process for reducing the amounts of zinc (zn) and lead (pb) in materials containing iron (fe)

Abstract

The present invention relates to a process for reducing the amounts of zinc and lead in starting materials comprising iron which comprises the steps of: —selectively leaching Zn and Pb comprised in the starting materials by mixing the starting materials with hydrochloric acid and an oxidizing agent comprising at least 5 wt-% of manganese dioxide in one or several reactor(s) at a temperature superior or equal to 35° C. and at a p H comprised between 0.5 and 3.5, —filtrating the mixture obtained in order to separate the solid and the filtrate, —washing the solid with water, the resulting solid comprising mainly Fe, a reduced amount of Zn and Pb compared to the original starting materials, —recovering the filtrate of step b) and the washing water of step c) which comprise chloride, solubilized Zn and Pb in one or several reactor(s), —precipitating solubilized Zn, Pb in the recovered filtrate and the washing water by mixing with a neutralizing agent, —filtrating and washing the solid residues obtained in step e) in order to remove the chloride from the solid residues which comprise at least Pb and Zn. The present invention also refers to the use of the materials obtained after treatment in a in a sinter plant and blast furnace or in all pyrometallurgical furnace which value iron such as electrical arc furnace (EAF), cupola furnace, oxycup furnace, submerged arc furnace (SAF), a plasma furnace, rotary hearth furnace.

1 .- 16 . (canceled) 
     
     
         17 . A process for reducing the amounts of zinc and lead in starting materials comprising iron, which comprises the steps of:
 a) selectively leaching Zn and Pb comprised in the starting materials by mixing the starting materials with hydrochloric acid and an oxidizing agent in one or several reactor(s) at a temperature superior or equal to 35° C. and at a pH comprised between 0.5 and 3.5,   b) filtrating the mixture obtained in order to separate the solid and the filtrate,   c) washing the solid with water, the resulting solid comprising mainly Fe and a reduced amount of Zn and Pb compared to the original starting materials,   d) recovering the filtrate of step b) and the washing water of step c) which comprise chloride, solubilized Zn and Pb in one or several reactor(s),   e) precipitating solubilized Zn, Pb in the recovered filtrate and the washing water by mixing with a neutralizing agent,   f) filtrating and washing the solid residues obtained in step e) in order to remove the chloride in solution from the solid residues which comprise at least Pb and Zn, wherein the oxidizing agent of step a) comprises at least 5 wt-% of manganese dioxide.   
     
     
         18 . The process according to  claim 17 , wherein manganese dioxide represents 10 to 100 wt-% of the total amount of oxidizing agent in step a). 
     
     
         19 . The process according to  claim 17 , wherein manganese dioxide represents 20 to 80 wt-% of the total amount of oxidizing agent in step a). 
     
     
         20 . The process according to  claim 17 , wherein manganese dioxide represents 25 to 50 wt-% of the total amount of oxidizing agent in step a). 
     
     
         21 . The process according to  claim 17 , wherein the oxidizing agent of step a) comprises one or more further oxidizing agents being selected from the group consisting of:
 air, oxygen, ozone, O 2  enriched air,   chlorine, hypochlorite, chlorite, chlorine dioxide, chlorate, perchlorate,   bromine,   potassium permanganate,   nitric acid,   dichromic acid,   hydrogen peroxide   and any combination thereof.   
     
     
         22 . The process according to  claim 17 , wherein the starting materials before the treatment comprise:
 from 1 to 55 wt-% of Fe,   from 0 to 65 wt-% of C,   from 0.01 to 30 wt-% of Zn, and   from 0.01 to 5 wt-% of Pb, based on the total weight of the starting materials.   
     
     
         23 . The process according to  claim 17 , wherein the treated materials comprise:
 from 0.9 to 60 wt-% of Fe,   from 0 to 70 wt-% of C,   less than 0.3 wt-% of Zn,   less than 0.1 wt-% of Pb, and   less than 1 wt-% of Cl, based on the total weight of the treated materials.   
     
     
         24 . The process according to  claim 17 , wherein the starting materials further comprise carbon. 
     
     
         25 . The process according to  claim 17 , wherein the leaching step a) is performed in a series of reactors. 
     
     
         26 . The process according to  claim 17 , wherein the neutralizing agent of step e) is selected from the group consisting of:
 lime, hydrated lime, limestone, milk of lime, milk of limestone,   caustic soda, potassium hydroxide,   sodium carbonate,   BOF slag,   the starting materials,   
       and any combination thereof. 
     
     
         27 . The process according to  claim 17 , wherein it comprises an additional step a′) between the steps a) and b) which consists in a selective precipitation of iron. 
     
     
         28 . The process according to  claim 27 , wherein the selective precipitation step a′) of iron comprises the addition of an oxidizing agent which is selected from the group consisting of:
 air, oxygen, ozone, O 2  enriched air, 
 chlorine, hypochlorite, chlorite, chlorine dioxide, chlorate, perchlorate 
 bromine, 
 manganese dioxide, potassium permanganate, 
 nitric acid, 
 dichromic acid, 
 hydrogen peroxide and any combination thereof, 
 
       and the addition of a neutralizing agent which is selected from the group consisting of:
 lime, hydrated lime, limestone, milk of lime, milk of limestone, 
 caustic soda, potassium hydroxide, 
 sodium carbonate, 
 BOF slag, 
 the starting materials and any combination thereof, in the mixture obtained after the leaching step a). 
 
     
     
         29 . The process according to  claim 26 , wherein O 2 , O 2  enriched air and/or air are injected to the recovered filtrate and washing water during the precipitation step e). 
     
     
         30 . The process according to  claim 17 , wherein Fe and manganese are solubilized at step a) and precipitated at step e). 
     
     
         31 . The process according to  claim 17 , wherein the pH at step e) is between 7 and  12 . 
     
     
         32 . The process according to any of  claims 17 , wherein the starting materials to be treated are blast furnace sludge, blast furnace dust, BOF sludge or BOF dust. 
     
     
         33 . The process according to  claim 17 , further comprising using the obtained treated materials obtained in a sinter plant, a blast furnace or in a pyrometallurgical furnace which values iron. 
     
     
         34 . The process according to  claim 17 , wherein the pyrometallurgical furnace is selected from electrical arc furnace (EAF), cupola furnace, oxycup furnace, submerged arc furnace (SAF), plasma furnace, and rotary hearth furnace.