Patent DE-102006021315-A1 (DE)
Title: Recovery of zinc-containing polymetallic raw materials, comprises blending the raw materials with a reactive, fine-grained carbon substrate, and dispersing a further portion of the raw materials in coarse-grained carbon substrates
Inventor: LOERKE PAUL
IPC: C22B19/38
Filed: 2006-05-02
Abstract: Recovery of zinc-containing polymetallic raw materials from a mixture of a calcium oxide-, calcium sulfate- and a carbon- substrate and energy carrier, and from the gas phase and the alkaline-adjusted agitated slag, comprises blending the raw materials with a reactive, fine-grained carbon substrate, and dispersing a further portion of the raw materials in coarse-grained carbon substrates. Recovery of zinc-containing polymetallic raw materials from a mixture of a calcium oxide-substrate used as a slag-forming material, calcium sulfate substrate and a carbon substrate used as a reducing agent and energy carrier in a rotary kiln with counter-current operational mode of feeding, and from the gas phase and the alkaline-adjusted agitated slag, by means of drying, preliminary milling, milling, mixing, pelletizing and step-wise thermal treatment using preheating, calcinating, reducing, final and cooling stage, comprises blending the raw materials with a reactive, fine-grained carbon substrate in a stoichiometric quantity proportion to all the carbon-depleting reactions in the solid feedstock, and dispersing a further portion of the raw materials in coarse-grained carbon substrates, which have an intermediate form between pellets and/or agglomerates, where (a) by means of a step-wise feeding of the calcium oxide substrate, a basicity of mol.% of calcium oxide+mol.% of magnesium oxide/mol.% of silica+mol.% of alumina+mol.% of ferric oxide is adjusted to 2-3, in the solid feedstock, firstly prior to the step-wise thermal treatment and then at its end in the final step of the rotary kiln; (b) the first portion of the calcium oxide substrate is fed prior to the thermal treatment that take place in a step-wise manner in the rotary kiln, at least in a quantity that is sufficient to bind the entire silica to alite 3CaO.SiO2 and alumina to 3CaO.Al2 O3 with 12CaO.7Al2 O3; (c) the second portion of the calcium oxide substrate is fed at the end of the thermal treatment in the final stage of the rotary kiln, at a quantity that is sufficient to bind the ferric oxide, which results from the reoxidation of Fe and FeO to e.g. 2CaO.Fe2 O3; (d) the calcium sulfate substrate is fed in the final and initial stages of cooling at the dissolid feedstock side of the rotary kiln, at a quantity in order to bind the resulting cement clinker minerals e.g., 2CaO.Fe2O3 to their sulfominerals e.g. 2(CaO.SiO2).CaSO4; (e) after the reducing thermal treatment in the reduction step of the rotary kiln, the solid feedstock with the supplied calcium oxide and calcium sulfate substrates is thermally treated by direct contact with cold air, preferably with the heat produced under oxidizing conditions in the final stage and subsequently in the cooling stage, where the metallic iron and iron oxide are reoxidized to ferric oxide and is bound in contact with CaO to e.g. 2CaO.Fe2O3 and is subsequently in contact with calcium sulfate substrate bound to sulfominerals; (f) the solid feedstock is heated under a partial pressure oxygen between 0.01-0.5 atmosphere in the final stage of rotary kiln and in the initial cooling stage to an agitation temperature of 1200-1450[deg]C, through which the zinc oxide is largely reduced by the metallic iron present in the solid feedstock and is reoxidized by evaporation and simultaneously through direct contact with the cold air, the residual metallic iron and FeO are reoxidized to Fe2O3, the carbon is completely combusted and the CaO and CaSO4 substrates are bound to cement minerals; (g) the total proportion of quantity of the carbon, which all the carbon-depleting reactions in the solid feedstock need at an agitation temperature in the reaction stage of less than 1250[deg]C, is adjusted in such a manner that by means of an autothermic reoxidation of the rest of the metallic iron and FeO to Fe2 O3 and a complete combustion of the carbon residue in agitated slag, the resulting energy potential is largely sufficient to accomplish the autogenous formation of cement clinker minerals; (h) hot air is blown as secondary air from the dissolid feedstock end of the rotary kiln furnace into the solid feedstock, after the cooling of the agitated slag through direct contact in the cooling stage with a temperature of 500-1000[deg]C in the final stage, where the total quantity of the cooling air is adjusted in such a manner that in the gas atmosphere of the rotary kiln and in the solid feedstock of the final stage of the rotary kiln, an over-stoichiometric ratio of oxygen to oxidizable constituents exists; and (i) the temperature profile of the cooling in the solid feedstock and the quantity of cold air for achieving direct contact is adjusted in such a manner that an autothermic reoxidation of the rest of the metallic iron and FeO to Fe2O and the complete combustion of the carbon residue is largely possible to a complete extent. An independent claim is included for a plant for the recovery of the zinc-containing polymetallic raw materials comprising a preliminary milling step, a milling step for grinding, a mixing stage for mixing of the raw materials, a pelletizing step for pelletizing the mixture, an oven for step-wise thermal treatment by preheating and deacidification of the solid feedstock in the preheating and calcinating steps, through the reduction in the reduction step and subsequent reoxidation of all the reduced solid feedstock and gas components in the final stage, where the zinc concentrate is obtained from the valuable metals that are driven into the gas phase of the rotary kiln through reductive combustion and cement clinker, which is obtained by supplying CaO and CaSO4 substrate to the solid feedstock residue that is obtained by reoxidative sintering taking place in the final stage of the rotary kiln, a cooling stage for completion of the cement clinker formation and cooling down of the cement clinker produced in the oven and the cooler and with a milling step for grinding the cement clinker with additives to form cement, where the cooling stage is composed of a heat exchanger or cooler (16), for cooling down the cement clinker through direct contact with air (17).