Basic Research And Application Of High-quality Brass Alloys By Recycling Scrap Copper

The recycling and utilization of copper scrap has not only alleviated the shortage of copper resources in China,but also solved the problem of accumulation of municipal solid waste.However,with the regulation of China’s import and export policy of scrap copper,as well as the large number of domestic scrap copper entering the market,the problem of more impurities and high impurity content in raw materials has become increasingly prominent.As a result,the applicability of traditional methods of pure material flushing and downgraded use for copper resource recycling is gradually decreasing.In this paper,the smelting process of brass alloy prepared from scrap copper was systematically studied in order to solve the problem of product quality caused by raw material composition.The main contents are as follows:Firstly,the thermodynamic analysis of the possible composition defects in brass alloy was performed.The effect of nonmetallic elements on the phase diagram of brass alloy and the solubility of trace elements in brass alloy were simulated.The defects of secondary brass ingot produced from scrap copper were analyzed.Based on the composition,the defects are divided into non-metallic inclusions and impurity elements.Non-metallic inclusions mainly include endogenous inclusions caused by chemical reactions and external inclusions caused by physical reasons.Endogenous inclusions include ZnO,ZnS,C,ZnCl2,Al2O3,SiO2,etc.,or intermediate compounds such as Na2S5 formed by refining agents reacting with non-metallic elements.The refining agent in this paper refers to the clearing inclusion flux(CIF)promoting the separation of non-metallic inclusions in the melt and the reaction agent removing impurity elements.External inclusions include slag,refractory,refining agent,etc.The defects caused by impurity elements are mainly composed of Pb,Sn,Bi,Fe,Ni.Al,Mn,Ni,Cr.etc.Secondly,aiming at the defect problem caused by non-metallic inclusions,based on thermodynamic simulation,a solid-liquid two-phase of the CIF suitable for secondary brass melt was studied.The effects of firing frequency,raw material structure and the CIF on ash amount,slag amount and the metal content in slag were investigated.When sodium fluosilicate(Na2SiF6)and calcium carbonate(CaCO3)are used as the CIF.the decomposition products are combined with non-metallic inclusions in the melt to form intermediate compounds,which have obvious purification ability for the secondary brass melt.The optimal mass ratio of Na2SiF6 and CaCO3 is 55:45.The optimal addition amount of CIF for smelting furnace is 2.0 wt.%,the optimal addition amount of CIF for intermediate furnace is 0.45 wt.%,the optimal addition amount of CIF for casting furnace is 0.375 wt.%,the optimal use time of CIF for intermediate furnace is 24 h,and the optimal use time of CIF for casting furnace is 36 h.This CIF has excellent effect on reducing ash amount,slag amount and the metal content in slag.Then,based on thermodynamic analysis,three purification methods of sulfurization-vacuum distillation,copper-calcium(Cu-Ca)alloy impurity removal and calcium boride(CaB6)impurity removal were proposed,including sulfurization-vacuum distillation impurity removal,Cu-Ca alloy impurity removal and CaB6 impurity removal.The effects of temperature,reaction time and additive dosage on the removal of elements were investigated.The results show that when the pressure is 30 Pa,the optimal conditions for the separation of impurity elements Pb,Sn and Zn from scrap copper by sulfurization-vacuum are temperature of 1050 0C,holding time of 60 min,and Cu2S addition dosage of 10 wt.%.Thus,the evaporation rates of Pb,Sn and Zn are 98.90%,99.02%and 99.44%,respectively.The optimal conditions for removing impurity elements Pb,Sn and Bi from the secondary brass by Cu-Ca alloy impurity removal method are temperature of 920℃,time of 60 min,Cu-Ca alloy addition dosage is 0.8 times of the theoretical addition dosage,and the optimal addition dosage of NaF is 2.0 wt.%.Thus,the removal ratios of impurity elements Pb,Sn and Bi are 47.71%,37.32%and 47.81%.respectively.The optimal conditions for the removal of impurity elements Fe,Ni,Al,Mn and Cr from secondary brass by CaB6 impurity removal method are temperature of 1020℃,reaction time of 120 min,and the addition dosage of CaB6 is 1.4 times of the theoretical addition dosage.Thus,the removal ratio of impurity elements Fe is 99.96%,the removal ratio of Ni is 76.62%,the removal ratio of Al is 99.18%.the removal ratio of Mn is 97.72%,and the removal ratio of Cr is 99.58%.The above impurity removal methods have achieved the synergistic treatment of multiple impurity elements in scrap copper,solving the key technical problem of turning waste into treasure when recycling.Finally,aiming at the problem of short service life of lining materials used in secondary brass smelting due to the adhesion of non-metallic inclusions and slag on the surface of side wall refractory and the deposition of furnace bottom,the corrosion behavior of side wall alumina-silica brick was studied with the aid of thermodynamic simulation.The results show that for every 100℃ increase in temperature,the corrosion mass of the side wall aluminum-silicon brick increases by 4.9*10"5%/day,and the corrosion time of a complete aluminum-silicon brick currently used is 41.40 days.The chemical reactions between the slag and the refractory are the main reason for corrosion behavior.Through comparative experiments of refractory corrosion process,it shows that silicon nitride and silicon carbide bonded bricks have strong corrosion resistance to secondary brass melt and slag.Increasing the content of mullite and TiO2,and reducing the content of Fe2O3 in the furnace bottom refractory are helpful to prolong the service life of the melting ditch.In response to the quality problems caused by the change of raw materials,this paper proposes an effective method for product quality improvement based on the traditional process of regenerating scrap copper for the preparation of brass alloys,and an optimization solution for the service life extension of refractory materials.Our research has enhanced the melting and casting process of high quality brass alloys from scrap copper,and most of the results have been applied in the enterprise,which has a good promotion prospect.