World of Metallurgy ERZMETALL 68 2015 No 3156 Paul B Queneau et al Recycling Lead and Zinc in the United States as miscellaneous materials recycled to either agriculture or chemicals Tables 4 5 and 6 Because the United States is a net importer of zinc 933 000 tons in 2013 only about 46 of the nation s total zinc consumption was derived from secondaries Table 4 3 1 Secondary zinc production and waste minimiza tion The focus below is on recycling U S secondary zinc for application in agriculture recycling zinc from electric arc furnace dust EAFD and via smelting leaching and electrowinning 3 1 1 Role of the agriculture and chemical industries The secondary zinc industry continues its efforts to mini mize the quantity of solid waste generated Brass mill and brass ingot plant flue dusts skimmings ZnO fines retort bottoms electrogalvanizer water treatment sludge and al kaline battery anode rejects are beneficially utilized by the fertilizer and zinc chemical industries Zinc rich flue dusts skimmings and ZnO fines containing 60 or more Zn are leached to produce zinc sulfate monohydrate zinc sulfate solution and zinc chloride see Table 5 and Table 6 Recy cling leady dust by product from bronze production is be coming increasingly difficult due to regulatory constraints The relatively pure zinc hydroxide cake recovered from electrogalvanizer outfall water treatment plants is par ticularly valued Substantial quantities of zinc hydroxide are calcined to produce oxide for agricultural markets as is off specification alkaline battery anode paste contains zinc dust potassium hydroxide and gelling agent Skimmings and similar mixtures of metal and oxides col lected at galvanizing plants pass through a preliminary physical separation step The processor buys skimmings and drosses from a number of customers and then sorts them by their source Large particles or blocks are broken using equipment such as pavement breakers drop weights or hammers Once the materials have been reduced in size they are fed to size reduction equipment such as hammer mills cage mills or ball mills to separate the metal from the oxide Air classification often used in the grinding equip ment allows easy separation on the basis of the differing densities of zinc metal and zinc oxide The lighter oxide particles are usually collected with cyclones or baghouses and are sold to other companies for further processing These oxides play an important role as a raw material for zinc fertilizers and other zinc chemicals The metallic parti cles are removed by screening and are set aside for remelt ing in one of a variety of furnaces Each type is described in detail in the following sections Old Bridge Chemicals Old Bridge NJ leaches ball mill fines produced by milling and screening skimmings raked from the surface of brass melts used to produce sheet and rod 18 19 Sulfuric acid leaching of these fines dissolves copper and zinc Solvent extraction then extracts the cop per most of which is converted to CuSO4 5H2O Traces of copper remaining in the zinc sulfate raffinate are cemented on zinc This solution is either spray dried or granulated Table 7 U S secondary zinc plants utilizing EAF dust from carbon steel 2014 Company location and capacity 2014 output tons a Technology and Comments Horsehead Holding Waelz Kilns Barnwell SC Two Waelz kilns 160 000 t a EAFD Electric Arc Furnace Dust capacity Calumet City IL Two Waelz kilns 169 000 t a EAFD capacity Palmerton PA 3 Waelz kilns 273 000 t a EAFD capacity 1 calcining kiln 155 000 t a Rockwood TN Two Waelz kilns 148 000 t a EAFD capacity Total EAFD capacity includes other metal bearing wastes e g from INMET CO was 750 000 t a averaging 20 Zn 630 000 tons EAFD were processed pro ducing CZO Crude Zinc Oxide contain ing 110 000 tons zinc Conversion of this CZO to zinc products was split between Monaca being shut down and Moores boro being started up A portion of the CZO was sold Conditioned EAFD is pelletized with carbon then reduced in a Waelz kiln 142 174 ft X 8 5 10 5 ft ID 1 100 C to volatilize the zinc which then oxidizes to CZO 53 Zn The iron rich kiln discharge solids 47 Fe 2 Zn are sold for as phalt aggregate or cement kiln fee CZO shipped to Palmerton for calcination drives off impurities Calcine zinc content is up to 63 0 5 Cl This granular product provided the Monaca smelter with its primary feedstock Zinc Nacional Waelz Kiln Millport AL Millport s two Waelz kilns 220 000 t a AFD capacity were established by Steel Dust Re cycling LLC SDR SDR was founded by Russ Robinson in 2007 Start up of the first kiln in 2008 was completed in three months Robinson sold SDR to Zinc Nacional Monterey Mexico in 2009 Key for Zinc Nacional was more closely servicing the U S steel industry Zinc Nacional retained the management team that built and operated SDR Mill port The plant s main product is Waelz Oxide CZO 62 Zn 5 Fe 4 Cl The CZO is transformed into zinc oxide zinc sulfate or zinc metal by zinc smelters The operation also markets its Waelz Iron Product WIP 39 Fe 10 CaO 2 Zn 1 S and 0 1 Cl Improvements in process efficiency include neu tral Waelz operation to minimize flux consumption while producing low leachability high Fe WIP WIP cooling in a rotary drum while preheating process air optimized dust settling CO post combustion and evaporative cooling two stage bag house op eration to include dioxin and mercury capture and wastewater free processing Half of Millport s CZO output is sold to Nyrstar s Clarksville TN smelter the balance is shipped to ZN in Mexico Horsehead Holding Zinc Refining Mooresboro NC In Jan 2014 this plant was in the start up mode Design capacity is 155 000 t a via zinc derived from secondaries principally CZO from its Waelz kilns Feedstocks include oxides de rived from milling zinc skimmings at its ThirtyOx plant in Forest City NC Metallics recovered at Thir tyOx are shipped to Imperial Zinc Chicago IL a joint venture partner Zinc metal output is PW SHG and CGG zinc Zinc oxide production is carried out at Horsehead s Zochem plant in Brampton Ontario Technicas Reunidas provided the leaching and solvent extrac tion SX technology The electrowinning EW melting and casting technology were licensed from Asturiana de Zinc Horsehead shut down 2013 2014 its Monaca smelter 136 000 t a Zn capacity transitioning to zinc metal production in Mooresboro The CZO is washed leached neutralized SX EW converts the pregnant liquor to zinc cathode Processing the leach residue plus custom materials produces lead smelter feed Advantages over Monaca are lower energy costs elimination of CZO decreased air borne emissions reduced operating maintenance and higher labor productivity

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