Refining of platinum group metals concentrates

Abstract

This invention relates to a process in which a Platinum Group Metal (PGM)-rich residue from a BMR (Base Metals Refinery) process is subjected to a high temperature roast to remove contaminants, typically volatile elements (for example Se, Te, As, S, Bi, Os) and obtain a roast product. The roast product is smelted with a flux to form a slag phase and an alloy phase, and to vaporize sulphates and heavy metals like Pb, Te, and remove stable oxide compounds such as Si02 and oxides of Fe, Ni, Co, Cu, Cr, Te, Bi to the slag phase. The alloy and the slag phase are separated, and the alloy phase is then melted and atomized with a gas or liquid atomization process to form fine alloy particles that can be dissolved in water and treated in a hydrometallurgical PMR (Precious Metals Refinery) process.

1 . A process in which a Platinum Group Metal (PGM)-rich residue, wherein greater than 40% by mass of Precious Metals in the residue are Platinum Group Metals (PGMs), containing less than 10% by weight base metals, is:
 subjected to a high temperature roast which includes an oxidative roast wherein the roasting temperature is above 500° C. and below 1000° C. to remove contaminants including Se, Te, As, S, Bi, Os and obtain a roast product; and   the roast product is smelted with a flux at a temperature of 1300° C. to 1600° C. to form a slag phase and an alloy phase, which are separated.   
     
     
         2 . The process as claimed in  claim 1 , wherein the roasting temperature is from 600° C. to below 900° C. 
     
     
         3 . The process as claimed in  claim 2 , wherein the roasting temperature is from 700° C. to 850° C. 
     
     
         4 . The process as claimed in  claim 1 , wherein an oxidation agent is added to the oxidation roast. 
     
     
         5 . The process as claimed in  claim 4 , wherein the oxidation agent is air. 
     
     
         6 . The process as claimed in  claim 5 , wherein from 100 to 150 g of air is added per 100 g residue. 
     
     
         7 . The process as claimed in  claim 6 , wherein from 130 to 150 g of air is added per 100 g residue. 
     
     
         8 . The process as claimed in  claim 1 , wherein the roasting step includes a reductive roast prior to or after the oxidative roast. 
     
     
         9 . The process as claimed in  claim 8 , wherein the reductive roast is carried out at a temperature of from 550° C. to 650° C. 
     
     
         10 . The process as claimed in  claim 9 , wherein the reductive roast is carried out at a temperature of about 600° C. 
     
     
         11 . The process as claimed in  claim 8 , wherein a reducing agent is added to the reductive roast. 
     
     
         12 . The process as claimed in  claim 11 , wherein the reducing agent is coal or petroleum coke. 
     
     
         13 . The process as claimed in  claim 1 , wherein the roast product is smelted at a temperature of 1400° C. to 1500° C. 
     
     
         14 . The process as claimed in  claim 13 , wherein the smelting is carried out under reducing conditions. 
     
     
         15 . The process as claimed in  claim 14 , wherein a reductant is added to the smelting step. 
     
     
         16 . The process as claimed in  claim 15 , wherein the reductant is a carbohydrate. 
     
     
         17 . The process as claimed in  claim 16 , wherein the reductant is flour. 
     
     
         18 . The process as claimed in  claim 17 , wherein 5 g to 15 g of flour is added per 100 g feed material. 
     
     
         19 . The process as claimed in  claim 1 , wherein the slag is a synthetic slag. 
     
     
         20 . The process as claimed in  claim 1 , wherein the flux is a Ca or Mg oxide, silicate, aluminate, alkali oxide flux. 
     
     
         21 . The process as claimed in  claim 20 , wherein the flux is a CaO—SiO 2 —Al 2 O 3 —Na 2 O flux. 
     
     
         22 . The process as claimed in  claim 21 , wherein the flux contains 10-40% by weight SiO 2 , 5-15% by weight Al 2 O 3 , 30-50% by weight CaO and 15-25% by weight Na 2 O. 
     
     
         23 . The process as claimed in  claim 1 , wherein the slag additions are from 20 g to 100 g slag per 100 g of roast product feed. 
     
     
         24 . The process as claimed in  claim 23 , wherein the slag additions are about 50 g slag per 100 g of roast product feed. 
     
     
         25 . The process as claimed in  claim 1 , wherein the smelting step is carried out without adding a collector. 
     
     
         26 . The process as claimed in  claim 1 , wherein induction is used to achieve smelting in a graphite receptor vessel lined with ceramic. 
     
     
         27 . The process claimed in  claim 1 , wherein the smelting is carried out in three steps:
 1) a reductive melting step;   2) lowering of pressure, preferably lowering the absolute pressure for a period of 10 to 30 minutes to remove Pb, Te and/or other heavy metals; and/or   3) addition of an oxidation agent such as K 2 NO 3 , Na 2 O 2 , O 2  gas, air NaNO 3  or MnO 2 , preferably NaNO 3  to ensure good partitioning of contaminants such as Fe and Ni to the slag phase.   
     
     
         28 . The process claimed in  claim 27 , wherein the absolute pressure lowered below 0.5 atm. 
     
     
         29 . The process claimed in  claim 28 , wherein the absolute pressure is lowered to about 0.1 atm. 
     
     
         30 . A process in which the alloy product of a process as defined in  claim 1  is melted and atomized with a gas or liquid atomization process to form fine alloy particles that can be dissolved in water and treated in a hydrometallurgical PMR (Precious Metals Refinery) process. 
     
     
         31 . A process as defined in  claim 1  carried out:
 after a Slow Cooling process, 
 in a Base Metals Recovery (BMR) process, or 
 in-between a BMR process and a PMR process