Patent Publication Number: US-2009217785-A1

Title: Method for separating impurities out of feed stock in copper melts

Description:
The present application claims the benefit of the filing date of Austrian Patent Application A1433/2005—filed Sep. 1, 2005, the disclosure of which is hereby incorporated herein by reference. 
     This invention relates to a method for separating impurities out of slag, dust, minerals, preparation residues of minerals or out of recyclings or remaining substances. All these substances to be purified are subsequently called feed stock. 
     Fusion metallurgy treatment methods in which iron melts are used to take up impurities are known for the purpose of separating impurities. A method of this type is described, for example, in AT 412 283 B. The aim of the method is to form environmentally compatible slag from iron-containing blast-furnace residue and to recover the iron fraction contained therein. For this purpose the residue is reduced in or over an iron melt by the carbon dissolved in the iron melt. Iron oxide and other metal oxides are reduced and recovered from the iron metal. After dephosphorization, the resulting metal can be used as a replacement for pig iron produced in a blast furnace or if the Cr/Ni contents are high, it can be used as a working resource for stainless steel production. The slag produced can be used as a clinker replacement in the cement industry. 
     According to WO 97/29214 A, residue or slag from rubbish incineration or pyrolysis is heated together with chlorine or chlorine-containing substances under reducing conditions to temperatures above 650° C. whereupon volatile metal chlorides such as heavy metal chlorides (PbCl 2 , ZnCl 2 , CuCl 2 ) are removed in the gas phase. The remaining solid residue is mixed with steel slag or lime marl. The mixed slag is reduced over a turbulent iron bath. In this case a synthetic blast furnace slag with hydraulic properties and a carbon-saturated iron alloy can be produced. The iron alloy obtained forms a feed stock for the steel industry. Alternatively a carbon-free, highly enriched ferro-chromium alloy can be obtained by fractional reduction. 
     JP 11207288 likewise describes a smelting method for the treatment of residue from rubbish incineration. In this case, the incineration residue is charged in an electric arc furnace into a metal bath which substantially consists of iron. A slag layer is thereby formed. Slag and metal are jointly extracted continuously and supplied to a water bath. Separation takes place by means of a magnetic separator. The metal contains a relatively large amount of copper and can be used as copper raw material. 
     In said methods which specify utilisation in the steel industry for contaminated iron melts, the enrichment by metals nobler than iron, for example, copper or tin is disadvantageous. These metals can no longer be removed economically and above certain limiting contents, present problems for further use of the iron melt. According to AT 412 283 B, for example, a high-quality pig iron bath system is used and this is contaminated with nobler metals after treatment of the residue. This deterioration in quality can have the result that use in the steel industry is no longer possible. 
     When using a pig iron bath system, an oxidising procedure has a disadvantageous effect. The carbon dissolved in the pig iron would thereby escape in the form of CO/CO 2  and thus the melting temperature would increase above 1500°. In order to prevent solidification of the melt when adding the residue, the required processing temperature must be significantly higher. At such high temperatures, the stressing of the refractory furnace lining and the increased energy requirement has a disadvantageous effect. 
     The purpose of the invention is to avoid these disadvantages and its object is to provide a method for separating impurities from slag, dust, minerals, preparation residues of minerals or from recyclings or remaining substances, subsequently called feed stock, in which deterioration in quality is avoided in a process extending over a fairly long time or in a plurality of successive process cycles. In addition, the method should allow energy savings compared with known methods and furthermore allow costs savings in that refractory linings of reactor vessels in which the process is carried out have a long life. 
     This object is achieved by the following combination of features:
         melting the feed stock containing the impurities;   forming a copper melt,   bringing the feed stock in contact with the copper melt while adding reducing agents, preferably coke or coal,   vaporising if required existing volatile compounds such as metal chlorides,   reducing metals of the feed stock more noble than copper in the copper melt and   forming a slag with constituents of the feed stock to be purified that is less noble than copper.       

     The copper melt preferably has a minimum content of 50% copper. 
     The use of a copper melt has the advantage that the impurities which cannot be removed from an iron melt can easily be removed from a copper melt in a normal copper recycling process. In this way, the contaminated copper melt can be processed to high-quality copper again. A particular advantage of using a copper melt is its low melting point compared to an iron melt. As a result, the processing temperature of the feed stock is primarily determined by the melting point of the slag. It is thereby possible to maintain low processing temperatures when carrying out the method, which is reflected in lower energy costs and in conservation of refractory linings of the metallurgical vessel in which the method is carried out. 
     The copper melt can optionally be purified by blowing oxygen directly into the metallurgical vessel in which the method is carried out. In this case, the impurities less noble than copper form a slag. As a result of its high copper content, the slag thus formed can be used for separating impurities from feed stock at the beginning of a following process. 
     It is particularly advantageous for the method according to the invention to use scrap copper for producing the copper melt since scrap copper is fed to the copper recycling process anyway. 
     The copper melt can be formed by melting copper-containing waste material. For this purpose new scrap (fabrication waste) and/or old scrap of copper and/or copper alloys can be formed. Part of the copper melt can be formed by adding slag produced by blowing oxygen into the copper melt, as has been mentioned above. 
     The slag formed from the feed stock to be purified is preferably processed using adjuvants and/or waste materials to form clinker substitute and/or sand blasting abrasives. 
     Dust from waste incineration and from the iron and steel industry can be used as feed stock to be purified. 
     Anodic sludge accumulating during electrolytic refining in the course of copper recycling is advantageously used as feed stock to be purified. 
     As has already been mentioned, preferably coke and/or coal are used as reducing agents for the feed stock but substances less noble that copper such as metallic waste materials e.g. aluminium-containing waste materials and/or iron-containing waste material can be used as reducing agents. 
     When using a copper melt, it is advantageously possible to adjust various atmospheres above said melt; both reducing and oxidising conditions can be adjusted. The atmosphere can also be varied over the duration of the process, whereby undesirable contents of the impurities can be specifically separated. 
     The feed stock to be purified together with the reducing agents are preferably injected into the copper melt. 
     The formation of a copper melt and the melting of the feed stock and the addition of the reducing agents can take place simultaneously or successively. For example, it is also possible that the feed stock to be purified is applied to a hot copper block which has not yet melted, preferably in layers, and any metal chlorides that may be present are thereby vaporised, whereby a halogenating atmosphere is preferably adjusted, preferably using a chlorine-containing flushing gas. 
     The copper block together with the feed stock to be purified is then melted and reducing agents are introduced into the melt, preferably are injected via lances. 
    
    
     The method according to the invention is explained in detail with reference to the description of two variants. The two variants show ways which are feasible in principle for using a copper melt. 
     Variant 1 
     The feed stock to be treated is injected into a copper melt located in a metallurgical vessel together with a reducing agent. Coal or coke, for example, can be used as reducing agents. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Reducing agents 
               
            
           
           
               
               
               
            
               
                   
                 Coke 
                 Coal 
               
               
                 Component 
                 [%] 
                 [%] 
               
               
                   
               
            
           
           
               
               
               
            
               
                 C 
                 91.15 
                 87.10 
               
               
                 SiO 2   
                 2.88 
                 2.20 
               
               
                 Al 2 O 3   
                 1.91 
                 1.25 
               
               
                 CaO 
                 0.36 
                 0.39 
               
               
                 MgO 
                 0.12 
                 0.09 
               
               
                   
               
            
           
         
       
     
     Metals in the feed stocks which are less noble than copper are also used as reducing agents. In addition, metallic reducing agents in the form of metallic waste materials, for example, aluminium or iron filings can be added, where the fraction of aluminium or iron is preferably at least 80%. 
     The copper melt is produced by melting copper-containing waste material. Predominantly considered for this purpose is new waste (fabrication waste) or old waste of copper and copper alloys (for example, brass, bronzes, red brass, nickel silver) including chippings and dust. The preferred copper content in the feed stock is at least 50%. Table 2 gives the composition of a brass and a bronze waste as examples. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Copper-containing waste material 
               
            
           
           
               
               
               
            
               
                   
                 Brass waste 
                 Bronze waste 
               
               
                 Element 
                 [%] 
                 [%] 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Cu 
                 60.19 
                 94.49 
               
               
                 Zn 
                 37.62 
               
               
                 Pb 
                 0.63 
               
               
                 Sn 
                 0.42 
                 4.77 
               
               
                 Fe 
                 0.2 
               
               
                 Al 
                 0.21 
                 0.039 
               
               
                 Ni 
                 0.13 
               
               
                 Si 
                 0.023 
                 0.016 
               
               
                 Sb 
                 0.006 
               
               
                 Mn 
                 0.038 
                 0.0023 
               
               
                 P 
                 0.007 
                 0.18 
               
               
                 As 
                 0.015 
               
               
                 S 
                   
                 0.21 
               
               
                 Pb 
                   
                 0.008 
               
               
                   
               
            
           
         
       
     
     The method according to the invention can be used to process contaminated dust, slag and minerals of different origin, in particular dust from rubbish incineration and slag or dust from the iron and steel industry. Lead or coloured glass waste, scrap catalysts and processing residue of minerals such as, for example, roasting residues (e.g. pyrite combustion) can also be used. Material cleared from furnaces which has been infiltrated with noble metals (e.g. Pt, Au, Ag) can also be processed with the method according to the invention. 
     In the course of copper recycling, the noble metals (Pt, Ag, Au) are deposited in the anodic sludge during electrolytic refining. The noble metals can be recovered from the anodic sludge by means of the method according to the invention and reused. Noble-metal-containing feed stock such as, for example, the aforementioned material cleared from furnaces thus make a decision contribution to improving the economic efficiency of a copper refinery. 
     Example compositions are given in the following tables: 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Dust from rubbish incineration 
               
            
           
           
               
               
               
            
               
                   
                 Fly ash from 
                 Fly ash from incineration 
               
               
                   
                 rubbish incineration 
                 of special rubbish 
               
               
                 Element 
                 [mg/kg] 
                 [mg/kg] 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Ca 
                 107000 
                 47985 
               
               
                 Cl 
                 74000 
                 33370 
               
               
                 Si 
                 160000 
                 54804 
               
               
                 Mg 
                 15000 
                 8041 
               
               
                 Fe 
                 25000 
                 43763 
               
               
                 Al 
                 71000 
                 17302 
               
               
                 K 
                 36000 
                 47485 
               
               
                 Na 
                 31000 
                 154364 
               
               
                 Zn 
                 28000 
                 68165 
               
               
                 S 
                 26000 
                 81929 
               
               
                 Pb 
                 11000 
                 19527 
               
               
                 Ti 
                 8700 
                 18332 
               
               
                 Mn 
                 1300 
                 1992 
               
               
                 Ba 
                 1700 
                 124 
               
               
                 Sn 
                 1400 
                 2741 
               
               
                 Cu 
                 1200 
                 6340 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Slag and dust from the iron and steel industry 
               
            
           
           
               
               
               
               
               
            
               
                   
                 LD 
                 EAF 
                 Blast furnace 
                 Converter 
               
               
                   
                 Slag 
                 dust 
                 dust 
                 dust 
               
               
                 Component 
                 [%] 
                 [%] 
                 [%] 
                 [%] 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 CaO 
                 50 
                  5-12 
                 6.3 
                 3-5 
               
               
                 SiO2 
                 15 
                   
                 6.3 
               
               
                 Al2O3 
                 &lt;2 
                   
                 2 
               
               
                 MgO 
                 &lt;3 
               
               
                 Fe 
                 16 
                 20-30 
                 34.4 
                 50-70 
               
               
                 MnO 
                 &lt;4 
               
               
                 P2O5 
                 &lt;2 
               
               
                 Cr tot   
                 &lt;1 
                 0.1-0.4 
               
               
                 C 
                   
                   
                 28.9 
                 20-50 
               
               
                 Pb 
                   
                 1-8 
                 0.07 
                 0.2-0.5 
               
               
                 Zn 
                   
                 15-35 
                 0.2 
                 1-3 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Residue from other branches of industry 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                 Catalytic 
               
               
                   
                 Pyrite 
                   
                   
                   
                 converter 
               
               
                   
                 combustion 
                   
                 Lead glass 
                   
                 (car indus- 
               
               
                   
                 (sulphuric acid 
                   
                 waste (glass 
                   
                 try) 
               
               
                   
                 production) [%] 
                   
                 industry) [%] 
                   
                 [%] 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Fe 
                 55 
                 SiO 2   
                 56 
                 Pt 
                 0.14 
               
               
                 Zn 
                 2.8 
                 PbO* 
                 32 
                 Pd 
                 0.07 
               
               
                 Cu 
                 1.3 
                 K 2 O 
                 11.4 
                 Rh 
                 0.015 
               
               
                 S 
                 2.6 
                 Al 2 O 3   
                 0.1 
                 Carrier 
                 Residue 
               
               
                   
                   
                   
                   
                 material 
               
               
                 Pb 
                 0.5 
                 As 2 O 5   
                 0.5 
               
               
                 Waste 
                 10.00 
               
               
                 rock 
               
               
                 Co 
                 0.12 
               
               
                 Ag 
                 0.004 
               
               
                 Au 
                 0.0001 
               
               
                 Cd 
                 0.005 
               
               
                 Tl 
                 0.003 
               
               
                 P 
                 0.11 
               
               
                   
               
               
                 *The PbO content can be 3-32% depending on the type of glass 
               
            
           
         
       
     
     The components of the feed stock are divided by the treatment process into copper bath, slag or waste gas according to their composition. 
     Metals in the feed stock which are nobler than copper are reduced and remain in the copper melt. Less noble components are transferred into the slag located above the melt. Volatile compounds in the feed stock such as, for example, metal chlorides, in particular zinc chloride and lead chloride, vaporise. 
     At the end of the treatment process the slag is adjusted with adjuvants or waste materials so that it can be used as clinker substitute or as sand blasting abrasive. The slag is then tapped and charged into a dry granulator. The granulation can take place by separating the slag stream on a rotary plate into fine droplets, which then solidify in a glass-like manner in the air stream. The copper melt is also tapped and fed to the copper recycling process whereby copper and the noble metals contained therein can be recovered from the melt. 
     The copper bath can optionally be purified by blowing oxygen directly into the melt system. The impurities which are less noble than copper thereby form slag. As a result of the high copper content, the slag thereby formed can be fed together with the scrap copper at the beginning of the process. 
     Variant 2 
     A block of scrap copper is heated in the melting system. Advantageously solidified residual copper melt from the previous treatment can be used for this. As in variant 1, the copper melt is produced by melting copper-containing waste material. The feed stock to be treated is applied in layers to the copper block. When using residual copper melt, charging can begin immediately after the surface of the copper bath has solidified. The heat of the cooling copper bath can be used to vaporise metal chlorides present in the feed stock. A halogenating atmosphere can be used for assistance, for example, using a chlorine-containing flushing gas. The flushing gas is blown onto the residue from above. Alternatively the residue can be roasted with chlorine or chlorine-containing substances under reducing conditions. 
     In this case, metal chlorides can be vaporised from the feed stock. The gas phase can be purified in the usual manner whereby the metal chlorides are retained in filters. The heavy metals can be recovered in a known manner (electrolysis, extraction). 
     The remaining metal compounds in the feed stocks can be removed by subsequent purification under reducing conditions. For this purpose the feed stock and the solidified copper melts are melted. Reducing agent is fed into the copper bath by means of lances (see Variant 1). 
     The copper melt and the slag can undergo further treatment as in variant 1.