【作者】 李景升；

【导师】 龚竹青；

【作者基本信息】 中南大学 ， 冶金物理化学， 2009， 博士

【摘要】 我国铋资源相当丰富,铋储量和产量均居世界第一位,但铋工业落后,尤其是铋深加工产品市场竞争力仍然较低。为将我国铋资源优势转化成产业优势,本文以某公司富含铋、锌、金、银的银锌渣为原料,提取并综合回收了其中有价金属,研究了银锌渣浸出液化学沉淀法制备高纯超细氧化铋的工艺,并在制备过程中控制粉体粒径,同时还探索了水热法制备超细氧化铋工艺。采用HCl+NaClO₃+NaCl体系浸出银锌渣,考察了浸出温度、浸出时间、液固比以及浸出液中各成分用量对铋浸出率的影响。浸出的适宜条件为液固比10:1,NaClO₃用量15g,NaCl用量60g,浓盐酸用量120mL,浸出温度80℃,浸出时间5h。在此条件下Bi的浸出率接近100%。为了还原浸出液中的少量银,可用新的银锌渣还原浸出液。在上述条件下浸出银锌渣,渣率为12%-16%,渣中银含量可达70%左右,金含量为1%。采用氨水浸银,水合肼还原制取海绵银,浸银渣再用氯酸钠加硫酸浸金,适宜条件下银、金的回收率均可达95%左右。从各金属的Me-Cl^--H₂O体系热力学计算,得到了Me-Cl^--H₂O系E-pH图,由此可以得出,对铋而言,控制溶液电位在0-1.4V的较宽范围内,当体系酸度较高（pH＜3）时,BiOCl将溶解;pH=3-11时,BiOCl有相当大的稳定区域。对于Ag和As,只要控制电位在一定范围内,pH值从-2到12范围内Ag和As均以离子形式存在,但Cl^-浓度太高,则Ag会以AgCl形式沉淀。对于Pb,在pH＜6,E＜1.4V的整个区域内,Pb均以PbCl₂形式存在,PbO₂^-的溶解要求很高的碱液浓度,在实践中难以实现。对于Fe,在没有氧化剂存在时,只要体系E＜0.6V,Fe以Fe²⁺形式存在,当pH＞6时才发生水解沉淀。当E为0.6-1.3V,控制pH＜1.4时,Fe可呈Fe³⁺形式从水解液中排出。对于Sb,当体系E＜0.8V,HCl浓度较高时,Sb呈SbCl₃形式存在,随着pH值升高,生成Sb（OH）₃,甚至生成Sb₂O₄,均为固相。提出银锌渣浸出液制备高纯三氧化二铋的工艺路线为“净化—水解—转化”。浸出液的净化工序为首先采用银锌渣除铅,控制初始pH值为0.3-0.4,银锌渣用量为100g/L,还原时间为15min,可使Pb降到3-10mg/L,过滤后在滤液中加少许NaI进一步除Ag,使Ag降到1mg/L左右后过滤得到净化后液。净化后浸出液水解制取BiOCl的适宜条件为体积比为8-10:1,中和剂为40%Na₂CO₃溶液或稀氨水,水解pH值为0.8,水解时间为20-30分钟。所得BiOCl用1 mol/L H₂SO₄溶液洗涤,再用蒸馏水或去离子水洗涤除Fe、Zn、Cu等杂质。BiOCl浓碱转化法制备三氧化二铋的适宜条件为液固比5:1,碱液浓度4mol/L,转化温度95℃,反应时间1h。所得Bi₂O₃用1mol/L NaOH溶液洗涤,再用去离子水洗涤,除去SO₄^2-和Cl^-等杂质离子,烘干即可得到高纯Bi₂O₃产品,在该条件下制备得到外形为四面体形或纺锤形的α-Bi₂O₃产品,产品粒径约为20μm,杂质含量很低,达到高纯三氧化二铋要求。Cu、As、Sb、Si含量都在十万分之几,Ag、Pb、Zn、Fe等金属杂质的含量都只有百万分之几。以上述方法得到的高纯粗颗粒氧化铋为原料,采用硝酸溶解,然后用氨水作沉淀剂,用化学沉淀法通过反滴加方式制备得到超细三氧化二铋粉体,其适宜工艺条件为硝酸铋浓度0.3mol/L,滴加速度2.5mL/min,氨水浓度1:10（体积比）,终点pH值9,搅拌速度600r/min。该条件下称取500g氧化铋进行放大实验,反应结束后过滤洗涤,在105℃干燥2h得到前驱体粉末,在马弗炉中于600℃下保温2h得到球状Bi₂O₃,计算表明其晶粒尺寸为28.6nm,SEM结果表明颗粒呈球形,颗粒大小比较均匀,平均粒径约为0.2μm。产品外观为橙黄色,色泽鲜艳,存在较为严重的团聚现象。从理论和实验上对氧化铋粉体的粒径进行了分析和控制,在成核初期采取变速滴加的方式可以产生爆发性形核,将形核过程控制在较短的时间内,实现形核和长大过程的分离,可获得较细的一次粒子。加入表面活性剂聚乙烯醇-124、油酸钠及十二烷基苯磺酸钠均可抑制颗粒团聚现象,其合适的用量分别为4×10^-3mol/L、0.8×10^-3mol/L、6g/L,该条件下分别加入三种表面活性剂,均可得到粒度分布较窄、分散性好的粒子,平均粒径分别约为0.05μm、0.07μm、0.123μm。聚乙烯醇分散剂控制团聚的作用机理为空间位阻作用,油酸钠和十二烷基磺酸钠控制团聚的机理为双电层（静电）稳定作用。分析了前驱体粉末干燥过程中产生团聚的原因,通过乙醇洗涤或正丁醇共沸蒸馏可有效地脱除湿粉末中残余水分子,阻止干燥过程中团聚的发生,获得了分散性较好、平均粒径分别为0.118μm和0.116μm的超细氧化铋粒子。分析和探索了水热法制备超细氧化铋粉体理论及工艺,研究了反应温度、时间、溶液填充度、溶液pH值以及反应介质种类等因素对晶体粒度和形貌的影响。温度越高,平均粒度越大,粒度分布越宽;反应时间较长,晶粒较粗,平均粒径较大;晶粒平均粒径随着溶液填充度的增大而减小;随着pH值增大,晶粒粒径变小;反应介质对晶粒尺寸的影响并不明显。水热法制备Bi₂O₃的适宜条件为反应温度为120℃,时间为2h,填充度为90%,溶液pH值为大于11。在适宜条件下所得Bi₂O₃的平均粒径大约为80nm,同时还发现改变反应体系pH值和反应介质可得到不同形貌和晶型的产品。更多还原

【Abstract】 Our country is in rich of bismuth resources of which the reserves and yields are in the first rank in the world.However,our country falls behind in the bismuth industry,and particularly the market competitiveness of deep-processing bismuth products is very weak.This work aims to transform this resource advantage to industrial advantage.The valuable metals of the raw material of silver-zinc slag containing substantial bismuth,zinc,gold and silver were extracted firstly,then the technology of preparing superfine bismuth oxide powder with high purity using chemical precipitation method was studied,as well as the technology of that with hydro-thermal method was explored.The key target of this paper is to control the particle size during the whole process.The solution containing HCl,NaClO₃ and NaCl was used to leach silver-zinc slag and the influences of liquid-to-solid ratio and the component dosage of leachate on the leaching rate of bismuth were investigated.The appropriate conditions of leaching silver-zinc slag are that the liquid-to-solid ratio is 10:1,the NaClO₃ quality is 15g,the NaCl quality is 60g,the HCl volume is 120mL,the extraction temperature is 80℃and the extraction time is 5h.The leaching rate of bismuth is 100% approximately,the slag yield is 12%-16%,the content of silver and gold of leaching residue reach 70%and 1%under these conditions.The silver was further extracted with hydrazine hydrate by reducing the residue that was leached by ammonia solution,and the gold was further extracted with NaClO₃ and H₂SO₄ solution from that leaching solution.The recovery rate of silver and gold gets up to 95%at right conditions.The Eh-pH diagrams of Me-Cl^--H₂O system were drawn based on thermodynamic equations of that system.For Bi-Cl^--H₂O system,if the solution potential（Eh） is in 0-1.4V,BiOCl will be dissolved when the acidity of solution is high（pH＜3） and be stable when pH =3-11.For Ag-Cl^--H₂O and As-Cl^--H₂O system,as long as Eh is controlled at a certain range,arsenic and silver exist in form of ion when pH value varies from -2 to 12,while if Cl^- concentration is too high,Ag will precipitate in form of AgCl.For Pb-Cl^--H₂O system,Pb exists in the form of PbCl₂ at the region of pH＜6 and Eh＜1.4V,it’s difficult for PbO2^- to dissolve because of the rigid demand of alkali concentration.For Fe-Cl^--H₂O system,Fe exists in the form of Fe²⁺ as long as Eh＜0.6V and there is no oxidizer,hydrolysis precipitation happens when pH＞6,and Fe can be removed in the form of Fe³⁺ when Eh is 0.6-1.3V and pH＜1.4.For Sb-Cl^--H₂O system,Sb exists in the form of SbCl₃ when Eh＜0.8V and HCl concentration is high,but solid Sb（OH）₃ and Sb₂O₄ form with the increase of pH value.The process route of the preparing high-pure bismuth oxide using chemical precipitation method with the leachate from silver-zinc slag was put forward.It is "purification-hydrolysis- transformation".The purification process is that the Pb is firstly removed to 3-10mg/L by silver-zinc slag under the conditions of pH value of 0.3-0.4,slag dosage of 100g/L and reaction time of 15min,and Ag is then removed to 1mg/L by a little NaI.The appropriate conditions of preparing BiOCl with purified solution using hydrolysis method are that liquid-to-solid ratio is 8-10:1,neutralizer is 40%Na₂CO₃ solution or dilute ammonia,pH value is 0.8 and the hydrolysis time is 20-30 min.The impurities of Fe,Zn,Cu and other impurities are removed by washing the BiOCl solid using 1 mol/L H₂SO₄ and deionized water.The appropriate conditions of preparing bismuth trioxide with BiOCl are that the liquid-to-solid ratio is 5:1,the alkali concentration is 4mol/L,the reaction temperature is 95℃and the reaction time is 1h.The impurities of SO₄^2- and Cl^- ions are removed by washing Bi₂O₃ solid using 1mol/L NaOH solution and deionized water.The product ofα-Bi₂O₃ with diamond shape and particle size of about 20μm is obtained at these conditions above.The content of Cu,As,Sb,Fe,Si of the product is a few parts in 100,000 and that of Ag,Pb,Zn,Fe is only a few ppm,which fulfils the requirement of high-purity bismuth trioxide.Superfine bismuth trioxide powder was prepared using chemical precipitation method by adding ammonia into Bi（NO₃）₃ solution that was prepared by HNO₃ and the coarse high-pure bismuth oxide obtained above.The appropriate conditions are that the Bi（NO₃）₃ concentration is 0.3mol/L,the feeding speed is 2.5mL/min,the ammonia concentration is 1:10（volume ratio）,the end pH value is 9 and the stirring rate is 600r/min.The preparation experiment in scale-up was carried out with 500g bismuth oxide at these conditions.The precursor powder of Bi（OH） ₃ is gained by drying the filter cake for 2h at 105℃.The spherical Bi₂O₃ is gained by roasting the precursor powder for 2h at 600℃.Its grain size is 28.6nm according to the calculation.SEM results show that the particles are spherical with the average size of about 0.2μm.The product has a bright orange color.The particles agglomerate seriously in the product.The particle size of bismuth oxide powder was analyzed and controlled from the aspects of theory and experiment.In the early nucleation period,the explosive nucleation occurs by feeding at varying rate.The nucleation process is controlled in a relatively short time,and a smaller particle is achieved by separating the process of nucleation and growth.The surfactant of PVA-124,sodium oleate and sodium dodecyl benzene sulfonate can inhibit agglomeration of particles,the appropriate dosage is 4×10^-3mol/L,0.8×10^-3mol/L and 6g/L respectively.The particle with narrower size and high dispersion ability can be obtained and its average particle size is 0.05μm,0.07μm and 0.123μm,respectively.The effect mechanism of polyvinyl alcohol on the agglomeration of particle is the steric clash function,and the effect mechanism of sodium oleate and sodium dodecyl sulfate is the dual-layer（static） stability function.The possible reason of agglomeration phenomena during the drying process was analyzed.It was found that the residues of water of wet powder can be removed and the reunion phenomena can be restrained by washing the powder with ethanol or azeotropic distillating with n-butanol.The particle with high dispersion ability is obtained under these operations and its average particle size is 0.118μm and 0.116μm respectively.The theory and technology of preparing superfine bismuth trioxide using hydro-thermal method were explored.The influences of reaction temperature,reaction time,filling degree,pH value,as well as such factors as the type of reaction medium on the crystal size and microstructure were investigated.The higher the temperature,the greater the average particle size,the wider the particle size is.The longer the reaction time,the coarser the grain,the larger average particle size is.The particle size decreases with the increase of pH value.The impact of reaction medium on grain size is not obvious.The appropriate conditions of preparing Bi₂O₃ with hydro-thermal method are that the reaction temperature is 120℃,the reaction time is 2h,filling degrees is 90%,the pH value is≥11.The average particle size obtained under these conditions is about 80nm.Meanwhile it was also found that the product with different microstructure and crystal can be obtained with the alteration of pH value and reaction medium.更多还原