World of Metallurgy ERZMETALL 68 2015 No 3 157 Paul B Queneau et al Recycling Lead and Zinc in the United States Old Bridge does both to produce ZnSO4 H2O powder and granules Annual outputs of monohydrate 35 5 Zn and liquid 11 5 to 12 Zn are 26 000 st and 1 200 st respectively see Table 7 Much of the monohydrate is consumed in animal feed premix The solution is consumed in fertilizer micronutrient formulations The other major U S producer of ZnSO4 H2O was Agrium Fairbury NE which shut down its plant in December 2013 Agrium leached a variety of zinc rich feedstocks in sulfuric acid High Grade Fines recovered from skim mings supplied by U S Zinc 1 3 of feed Waelz kiln washed CZO 1 3 of feed brass ingot dust 1 5 of feed plus French and American process oxides Lead tin and silver reported to the leach residue This filter cake can be shipped as is to a primary lead smelter ideally after converting the lead sulfate to lead carbonate using aque ous sodium carbonate Problems with recycling the cake included the low lead content the presence of tin and the high shipping cost The zinc sulfate leach liquor was purified by cementation on zinc dust to reject copper and cadmium Agrium then produced granular monohydrate 25 000 t a of monohydrate via fluid bed granulation Monohydrate powder was produced via spray drying The company also outputted liquid zinc sulfate 10 000 t a 11 5 to 12 Zn see Table 5 The zinc micronutrient industry in addition to producing zinc sulfate solution zinc sulfate monohydrate zinc oxide and zinc iron sulfate crystals also produces granulated zinc oxysulfate see Table 5 Oxysulfate is partially sulfated oxide Solid byproducts containing 20 to 60 Zn are gran ulated with concentrated sulfuric acid and a little water to produce zinc oxysulfate micronutrient This procedure provides an important outlet for zinc bearing materials that are too low in grade to be economically processed for direct metal recovery or metal salt recovery The oxysulfate granules are normally produced in disc or drum granula tors The feedstock in combination with acid and water is blended sulfated and rolled so that the particles grow with multi layer skins like an onion or a hail stone The gran ules are dried typically in a rotary kiln or fluid bed then screened The oversize typically 6 mesh about 15 of the feed is hammermilled to 1 8 inch then is returned to the granulator as are the dust and undersize typically 12 mesh about 30 of the feed Agronomic studies show that at least 50 of the zinc in the oxysulfate product should be sulfated to be readily available as micronutrient fertilizer 20 Unsulfated ZnO is acceptable if it is sufficiently fine and if it is applied to the soil well before the zinc is needed by the plant lead time is principally a function of soil pH and temperature Heavy metals particularly lead and cadmium are a serious concern whether guidelines used by the fertilizer industry and government regulators are appropriate is beyond the scope of this paper 21 Zinc chloride serves as an excellent source of zinc in liquid fertilizer Ammonia addition provides nitrogen plus makes the mix sufficiently non corrosive for storage in carbon steel Zinc sulfate addition provides sulfur secondary nu trient The chloride is twice as soluble as the sulfate but the cost of zinc sulfate is half that of the chloride The greater the shipping distance the higher the chloride to sulfate ratio thus increasing solution zinc content from 10 up to 20 ZnCl 2 solution is also added to zinc oxysulfate granulators to increase both granule zinc concentration and granule particulate cohesion Zinc chloride for fertilizer is manu factured by leaching various sources of ZnO secondaries with byproduct HCl Alternatively byproduct ZnCl2 is pro duced by Honeywell Baton Rouge when manufactur ing CTFE monomer chlorotrifluoroethylene powdered metallic zinc is used as a reductant in the manufacturing process Zaclon Cleveland OH reacts ZnO to produce ZnNH4Cl flux for steel galvanizers see Table 6 3 1 2 Recycling Electric Arc Furnace Dust EAFD in Waelz Kilns Horsehead Holdings and Zinc Nacional operate Waelz kilns to recycle EAFD see Table 7 Horsehead operates these kilns to volatilize zinc from iron rich zinc by products averaging 20 Zn Barnwell SC Calumet City IL Palmerton PA and Rockwood TN Zinc oxide is carbothermically reduced to zinc metal which volatilizes then burns to ZnO dust above the tumbling car bon rich bed The ZnO rich dust is swept by the furnace gases into baghouses Furnace products are Calcined Zinc Oxide CZO 53 Zn and Waelz Iron Product WIP 47 Fe and 2 Zn Until late 2014 Horsehead up graded most of its CZO in a second kiln under oxidizing conditions to fume off Pb Cd and halides generating an enriched ZnO calcine 63 Zn Horsehead s calcine and a portion of the CZO were shipped to its Monaca PA smelter along with purchased zinc secondaries 22 24 Feedstocks delivered to Monaca were converted to zinc metal zinc oxide zinc powder and zinc dust Table 8 The CZO was washed in water to remove soluble impuri ties prior to sintering Feeding the washed sintered oxide along with new and reclaimed coke flux blue powder plant drosses output from physical classification and pur chased secondaries to electrothermic furnaces produced prime western zinc pw 0 9 Pb An onsite 110 MW coal fired power plant provided the electricity Column distillation the prime western rejected lead and residual impurities to generate SHG and SSHG Special Special High Grade zinc slab plus cadmium metal byproduct A portion of the distilled zinc was burnt to oxide Larvik furnaces processed plant dross byproduct in combination with SHG zinc and purchased secondaries Furnace offgas outputs were condensed to produce zinc dust or burnt to zinc oxide Low iron plant dross was Larviked separately to permit a low temperature lead tap Larviks that were fed high iron metallic drosses required a high temperature iron tap described below in the Secondary Zinc Smelters section Zinc Nacional operates two Waelz kilns at Millport AL 25 About half of its CZO output is sold to the Nyrstar

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