Lead Refining/alloying

LEAD REFINING PROCESS 

The lead received from Rotary Furnace is called hard lead /crude lead .The lead tapped from the furnace has to  be  cleaned  from  residual  oxides  and slag. After stirring for a while the impurities settle at the surface and are skimmed off .

Crude  lead  originating  from  battery  scrap is  normally  alloyed  with  copper  andantimony  and also some traces  of  Ca,  Sn,  As,  Zn. In order to remove the unwanted elementsBy  adding sulphur  to  the  lead  melt  and  after  stirring  for  some  time,  a  Pb/Cu2S-dross  (and  if  present  with  minor  parts  of  Zn,  Sb,  As)  is  formed  and  skimmed  off.

This  de- copperisation     step  should  be carried out at least two times or more to secure the refining result.The  de-copperised  lead  still  contains  a large  amount  of  antimony  (and  maybe some  Sn,  As).  All  of  these  elements  can be removed by oxidation. For that purpose air or oxygen-enriched air is blown into the  melt  and  stirred.  The  different  oxides formed  settle  at  the  surface  and  can  be skimmed  off.  The  oxidizing  process  is completed  when  mainly  lead  oxide  is formed.  Instead  of  oxidizing  the  impurities  by injecting  air,  sodium  nitrate  (NaNO3) can be  added.  Here  again  a  dross  containing the  impurities  (and  lead)  is  formed,  which  is  skimmed  off  after wards.  All  refining  by-produced or residues should be processed to  recover  lead  and  other  valuables components.

 The  refining  processes  and  the  purity  of the refined lead are monitored by chemical analysis.