奥托昆普哈贾瓦尔塔精炼厂镍电解工艺 (1).doc

Nickel electrolysis process at Outokumpu Harjavalta Metals Oy奥托昆普哈贾瓦尔塔金属公司镍电解工艺AbstractThis paper deals with the electrolysis of nickel from sulphate solution and its electrochemical principles. As an example, the nickel electrolysis process at Outokumpu Harjavalta Metals Oy is discussed in more detail. The leaching of nickel matte and the purification of the nickel sulphate solution prior to electrolysis is also discussed. In addition, a short review of other hydrometallurgical nickel matte treatment processes and nickel electrolysis technologies is given.摘要： 本论文主要研究了硫酸镍溶液的电解过程及其电化学原理。作为例子，本论文主要在细节方面讨论了奥托昆普哈贾瓦尔塔金属公司的镍电解过程。同时也讨论了电解过程之前的镍浸出及净化过程。除此之外，其它镍湿法冶金处理过程及电解技术也在文中涉及到。Outokumpu has produced electrolytic nickel at Harjavaita works since 1960. Nickel is electrowon from a nickel sulphate solution using diaphragm cells where a diaphragm cloth is used to prevent the catholyte solution and the acidic anolyte from mixing. Nickel is deposited on thin nickel starter sheets and the anodes are of unalloyed lead. The current density is 200 A/m2 and the deposition time is seven days. The ready cathodes weigh about 65 kg and they are harvested, washed and cut into squares and strips and finally packed for delivery. Electrolytic nickel is supplied to the electroplating, melting and superalloying industry.早在1960年开始，奥托昆普便在哈贾瓦尔塔工厂开始生产电解镍。电解镍是从硫酸镍溶液中用隔膜电解槽电解产出的，而隔膜布的作用是防止阴极液和阳极液混合。电镍在很薄的始极片上沉积，而阳极是纯铅阳极。阴极电流密度为200A/m2，阴极周期为7天。达到生产周期的电解镍约65 kg，经出槽、烫洗后剪切成方块和条状，最终包装并发送至客户厂家。电解镍主要用在电镀、熔炼和超耐热合金等领域。In addition to nickel cathodes, Outokumpu has also been producing nickel briquettes since the last expansion in 1995. The expansion of the nickel production has also brought about several process changes in the smelter and the refinery. The smelter now produces two types of nickel mattes, which are treated in separate leaching plants. After leaching, the nickel solution is treated in a new solvent extraction step to produce a purified nickel sulphate solution for electrolysis and hydrogen reduction. The annual capacity of the nickel plant is 18,000 tons of cathodes and 22,000 tons of briquettes. 除电解镍之外，奥托昆普从1995年扩建之后也开始生产镍砖。这次扩建对冶炼厂和精炼厂都带来了很多的技术改革。冶炼厂现生产两种类型的冰镍，分别用不同的浸出装置处理。浸出后，含镍溶液在新的溶剂萃取工序处理，并产出纯净硫酸镍溶液用来进行电解和氢还原。镍厂生产能力为18000 t/a的电解镍和22000 t/a的镍砖。1. IntroductionNickel is an important alloying element in the metal industry. More than 70% of the nickel is consumed in stainless and alloying steels /1/. Other main uses of nickel are non-ferrous alloys (11%) and corrosion resistant and decorative plated coatings (8%). The world primary nickel demand was 928000 tons in 1996 /2/.1、简介 镍是金属工业中一种非常重要的元素。超过70%的镍消费于不锈钢行业和合金行业（文献1）。镍的其它用途有非铁合金（11%）和防腐蚀以及装饰性电镀（8%）。在1996年，全球镍需求量为92.8万吨/年（文献2）。Nickel is refined from sulphide or laterite ores. About 60% of the nickel is mined from sulphide deposits and 40% from laterite deposits /3/. In laterite ores nickel is bound in iron oxide or silica compounds from which it is difficult to upgrade. Therefore, direct smelting of ore is generally used to produce ferronickel or nickel matte. Direct leaching of laterite with ammonia or sulphuric acid is also used. Studies on the hydrometallurgical processing of laterite ores have been very numerous recently and various new leaching and refining processes have been proposed. Also, several mining projects on laterites are under way. 镍主要从硫化矿或红土矿中提取。目前约60%的镍是从硫化矿中提取，40%的镍从红土矿中提取（文献3）。由于红土矿中镍表面被氧化铁或氧化硅覆盖而难以提炼，因此矿石被直接冶炼生产镍铁或冰镍。也可从红土矿中由氨或硫酸直接进行镍浸出。目前对于红土矿湿法冶金过程有很多研究，并且提出了很多新的浸出和精炼过程。同时，很多公司正在开展红土矿采矿工程。Typical nickel-containing sulphide minerals are pentlandite (Ni,Fe)9S8, pyrrhotite Fe1-xS and millerite NiS. Nickel-bearing sulphide ores can be concentrated e.g. by flotation to upgrade the nickel content. Nickel concentrates, generally containing 7-25% Ni, are recovered. The nickel concentrates are usually smelted to charge the iron and magnesium oxide of the concentrate into an iron silicate slag. The nickel is recovered into a sulphide matte containing 35-70% Ni. The main minerals of the matte are heazlewoodite Ni3S2, chalcocite Cu2S and a Ni-Cu alloy. Important side metals of the nickel mattes are cobalt, copper and platinum group metals. 典型的含镍硫化矿有镍黄铁矿(Ni, Fe)9S8、磁黄铁矿Fe1-xS和针镍硫矿NiS。硫化镍矿可以通过浮选来浓缩并提升镍含量，获得含Ni约725%的镍精矿。镍精矿一般通过冶炼富集其中的铁和氧化镁，并将其转化为硅酸铁炉渣。镍则成为含Ni 3570%的硫化冰镍。冰镍中主要含有六方硫镍矿Ni3S2、辉铜矿Cu2S和Ni-Cu合金。冰镍中含有的其它主要金属有钴、铜和铂族金属。Because of valuable side metals and also because of harmful impurity elements, nickel matte must go through a multi-stage refining process. Generally, matte is treated by hydrometallurgy consisting of oxidation of matte in leaching or in electrorefining, purification of the nickel solution and recovery of high grade metallic nickel by electrolysis or hydrogen reduction. 由于冰镍中含有很多其它金属，并且很多金属为有害金属，因此冰镍必须经过一个多级精炼过程。一般来说，冰镍需经过由冰镍氧化浸出或电解、镍溶液提纯组成的湿法冶金流程，再通过电解或氢还原工艺得到高等级的金属镍。2. Hydrometallurgical matte refining processesHydrometallurgical processes to refine nickel matte can be specified as follows /4,5,6,7,8/:1) Matte electrolysis. Cast nickel matte anodes are dissolved in a diaphragm electrolysis cell using a chloride/sulphate electrolyte. The electrolyte from the anode compartment is circulated through the solution purification before feeding to the cathode bag. Also the anodes are bagged to collect the sulphur-containing anode slime of the anode. The process is in use at Incos Thompson refinery in Canada /9/.2、冰镍精炼湿法冶金过程以下是几种冰镍精炼湿法过程的详细说明（文献4、5、6、7、8）：1）冰镍电解。将冰镍浇筑成阳极板并在隔膜电解槽中用氯化物-硫酸盐溶液进行电解。阳极液循环经过溶液净化过程后再进入隔膜袋进行电解。阳极同样套袋以收集含有硫磺的阳极泥。加拿大Inco公司汤普森精炼厂便采用此流程。2) Chloride leach process of matte and electrowinning. Matte is leached in a chloride solution using chlorine gas as an oxidant. The chlorine gas is generated in the electrowinning cells. The process is in operation e.g. at Falconbridges refinery in Kristiansand in Norway, Sumitomos Niihama refinery in Japan and at Eramets refinery in Sandouville in France /9, 10, 11, 12, 13/.2）冰镍氯化浸出-电解流程。冰镍在氯化物溶液中使用氯气作为氧化剂进行浸出。氯气是在电解过程中产出的副产物。挪威克里斯蒂安松鹰桥精炼厂、日本住友新居滨精炼厂和法国桑杜维尔埃赫曼精炼厂都采用这一流程。3) Atmospheric acid leach and electrowinning. Matte is leached in acid sulphate solution in oxygen or air-sparged leach vessels. After the atmospheric leach, a two-stage pressure leach follows to decrease the nickel content in the residue and to oxidise a portion of the copper sulphide to circulate the dissolved copper in atmospheric leaching. The nickel sulphate solution is purified by solvent extraction or by cobaltic hydroxide precipitation. The nickel is precipitated as cathodes in the electrowinning process. The atmospheric acid leach and the sulphate electrowinning process have been developed by Outokumpu Oy and these methods are used e.g. by Bindura, Empress and Hartley refineries in Zimbabwe and by Outokumpu at Harjavaita Works in Finland /4,5,14/.3）常压酸浸-电解流程。冰镍在氧气或空气喷射入浸出槽中，并用硫酸溶液进行浸出。常压浸出后，继续进行两段加压浸出，以降低浸出渣中镍含量，同时将一部分硫化铜氧化，并将溶解的铜返回常压浸出。硫酸镍溶液通过溶剂萃取法或钴的氢氧化物沉淀法净化。经净化后的溶液在电解工序产出电解镍。常压酸浸-硫酸镍电解流程是奥托昆普公司研发的，津巴布韦的Bindura、Empress和Hartley精炼厂以及芬兰奥托昆普哈贾瓦尔塔厂均采用这一流程。4) Ammonia pressure leach and hydrogen reduction. Matte is leached into ammoniacal ammonium sulphate solution in pressure autoclaves using air as an oxidant. After the sulphide precipitation of copper, nickel solution is reduced with hydrogen in the reduction autoclaves to produce metallic nickel powder. The ammonium sulphate forming in the hydrogen reduction is recovered by crystallisation. After the hydrogen reduction the rest of the dissolved nickel and all the cobalt are precipitated with hydrogen sulphide. This process is known as the Sherritt Gordon Process /15/ and it is applied at Sherritts Fort Saskatchewan plant in Canada and at WMCs Kwinana refinery in Australia.4）加压氨浸和氢还原。冰镍在加压浸出釜中以硫酸铵溶液并通入空气作为氧化剂进行浸出。经过硫化物除铜，含镍溶液在还原釜中用氢气还原生成金属镍粉。氢还原过程中生成的硫酸铵通过结晶回收。经过氢还原后，游离的镍和所有的钴用硫化氢气体沉淀。这一过程便是谢里特戈登法，加拿大谢里特的福特萨斯喀彻温厂和澳大利亚奎那那厂均使用这一方法。5）Acid pressure leach and hydrogen reduction. Matte is leached with spent copper electrowinning electrolyte using pressure autoclaves and air as an oxidant. After the leaching, copper and iron are precipitated. Then the nickel solution is ammoniated for hydrogen reduction. The process was developed by Sherritt Gordon and is operated e.g. by Impala Platinum in South Africa /8/. Rustenburg Platinum in South Africa also uses the acid pressure leach but metallic nickel is deposited with the electrowinning process /16, 17/.5）加压酸浸和氢还原。冰镍在加压釜中用废铜电解液并通入空气作为氧化剂进行浸出。浸出后，铜和铁被沉淀，含镍溶液被氨化以备氢还原。这一流程是由谢里特戈登研发出的。南非因帕拉铂金厂便使用此法（文献8）。南非里斯腾堡铂金厂同样应用加压酸浸法，但通过电解法生产电镍（文献16,17）。3. Nickel electrolysis processesAll electrolytic nickel production processes use a diaphragm cell originally developed by Norwegian chemist N.V. Hybinette at the beginning of 1900s /18/. The Hybinette cell was developed for electrolytic refining of cast matte anodes. In the cell, the anode and cathode are separated by a permeable diaphragm cloth. The matte anode dissolves in the anode bag and the electrolyte with the dissolved impurities of the anode is fed to solution purification. The purified nickel solution is fed into the cathode compartment of the electrolysis cell. The hydrostatic pressure difference between cathode and anode solutions prevents the solutions from mixing. The Hybinette process was first introduced at the Kristiansand refinery where matte refining electrolysis was introduced in 1910.3、镍电解流程 所有的镍电解流程都使用隔膜电解法，这一方法是挪威化学家N.Y. Hybinette在1900年左右首先提出的。Hybinette电解槽开始时是为冰镍浇筑阳极（可溶阳极）而研发的。电解槽中，阳极和阴极用一个具有渗透性的隔膜布隔开。冰镍阳极在阳极袋中溶解，含有各类杂质的电解液进入溶液净化工序。经过净化后的电解液进入电解槽的阴极室。溶液静压力的不同阻止了阴极液和阳极液混合。Hybinette电解流程于1910年首先在克里斯蒂安松精炼厂使用。3.1 Matte electrolysisMatte electrolysis is carried out in a mixed chloride-sulphate solution. The principal anodic reaction is oxidation of heazlewoodite, as shown in reaction (1). On the surface of the anode a sulphur-containing anode layer is formed. The sulphur layer causes anodic polarisation as the anode dissolves.3.1 冰镍电解冰镍电解是在氯化物-硫酸盐混酸体系中进行的。主要的阳极反应是Ni3S2的氧化，如方程式（1）所示。随着反应进行，阳极表面形成一层含硫层（阳极泥）。阳极泥层在阳极溶解过程中引起阳极极化。Ni3S2 = 3Ni2+ + 2S0 + 6e-(1)At Incos Thompson refinery the anodes weigh about 250 kg /9/. The current density is 240 A/m2 and the voltage is 3-6 V, depending on the slime layer thickness of the matte anode. The purified electrolyte contains 75 g/L Ni2+, 51 g/L Cl- and 120 g/L S042-. Boric acid is added to buffer the pH of the electrolyte. The cathode cycle is 10 days and the anode cycle is 15 days. More nickel is deposited at the cathode than is dissolved at the anode. To keep the nickel balance in the solution, a portion of ground matte is leached in the air-agitated reactors. The capacity of the Thompson refinery is 55,000 tpa nickel.Inco公司汤普森精炼厂的阳极约重250 kg（文献9）。电流密度为240 A/m2，槽电压为36V，槽电压取决于阳极泥厚度。净化后的电解液含有75 g/L Ni2+、51 g/L Cl- 和120 g/L S042-。电解液中加入硼酸作为pH值缓冲剂。阴极周期为10天，阳极周期为15天。阴极上沉积的镍要比阳极溶解的镍多。为保证溶液体系镍平衡，在空气搅拌槽中浸出一部分磨细的冰镍。汤普森精炼厂年产电解镍55000 t。3.2 Chloride electrowinningThe Falconbridge Chlorine Leach Process was installed at Kristiansand refinery at the end of the 1970s to replace matte electrolysis /10, 11/. The anodic reaction of the electrolysis is the evolution of chlorine gas, which is used as an oxidant in the leaching of ground matte. After leaching, iron is precipitated. Cobalt is recovered by solvent extraction and electrowinning. The nickel solution from leaching contains 230 g/L nickel which is diluted with the dechlorinated anolyte to 85 g/L. After the final purification the nickel chloride solution is fed to the EW tanks. Anodes are separated from the cathode cell compartment with a diaphragm. The chlorine gas vacuum in the anode side keeps the hydrostatic head and the catholyte flows to the anode compartment. The anodes are DSA anodes (dimensional stable anodes). The capacity of the tankhouse is 68,000 tpa as cathodes and crowns.3.2 氯化电积 二十世纪七十年代末期，鹰桥氯化浸出工艺在克里斯蒂安松精炼厂应用，并取代了冰镍电解流程（文献10,11）。电积过程的阳极反应是氯气的析出，氯气回收后作为磨细冰镍浸出的氧化剂。浸出后，铁被沉淀。钴被溶剂萃取回收并以电解方法产出。浸出液中含镍为230 g/L，用除氯后的阳极液稀释至85 g/L。在最终净化后，氯化镍溶液进入电积槽阴极室。阳极和阴极用隔膜袋隔开。阳极产生的氯气被抽出以保证阳极室内静压头较小，阴极液流入阳极室内。阳极是DSA阳极（固定尺寸阳极）。电解产能为每年68000 t的电积镍和镍冠。Sumitomo changed from the matte electrolysis process to Matte Chlorine Leach and Electrowinning (MCLE) at its Niihama refinery in 1993 /12/. The outline of the process is in principal the same as in the Falconbridge process. Copper is removed as a form of copper powder by electrowinning. Cobalt and iron are removed as hydroxide precipitate using Cl2 as an oxidant and by neutralising with nickel carbonate. 1993年，日本住友公司新居滨精炼厂将其冰镍电解流程改为冰镍氯气浸出-电积流程（MCLE）（文献12）。其主要流程与鹰桥流程基本相同。铜杂质是用电解法生产铜粉而除去。钴和铁杂质是用Cl2作为氧化剂并通入碳酸镍中和水解除去。The MCLE cells are equipped with DSA anodes and each cell has 53 anodes and 52 cathodes /13/. Electrolyte is fed from one side of the cell and about 30% of the feed electrolyte overflows from the other side. The rest of the electrolyte passes through the diaphragm bag into the anode compartment and is withdrawn by vacuum with chlorine gas generated at the anode. The electrolyte contains 70 g/L Ni2+ and 85 g/L Cl-. About 10 g/L nickel is deposited in the EW circuit. Nickel is deposited on the starting sheet plates that are deposited on a titanium mother blank. The current density is in the range of 230-250 A/m2 and the cell voltage is 3.1 V. The cathode life is 7 or 8 days, depending on the current density. The tankhouse has 168 nickel electrolysis cells. The production capacity is 30,000 tpa. 冰镍氯气浸出-电积流程的电积槽中使用固定尺寸阳极，每个电积槽有53块阳极和52块阴极（文献13）。电解液从阴极室的一侧流入，约30%的阴极液会从另一侧溢出流走。剩余的阴极液经过隔膜袋进入阳极室，并随着阳极产生的氯气被抽真空抽走。阴极液含有70 g/L Ni2+ 和85 g/L Cl-。约10 g/L的Ni2+在阴极沉积。镍是在用钛种板产出的始极片上面沉积。电流密度为230250 A/m2，槽电压为3.1V。阴极周期为78天，根据电流密度而定。电积厂房有168个电积槽，年产量为30000 t。Eramets nickel refinery in Sandouville, France also uses a chloride electrowinning process /9/. The refinery was commissioned in 1978. In leaching of matte the lixiviant is ferric chloride and iron is reoxidised using chlorine gas from the anode compartment of the electrolysis cell. Ferric iron is extracted from the nickel chloride solution by solvent extraction, is stripped and recycled to leach. Cobalt is also recovered with solvent extraction. Nickel is deposited as cathode plates using the starter sheet method. The tankhouse has 80 cells and the capacity is 13,000 tpa nickel cathodes. 法国桑杜维尔埃赫曼精炼厂同样也采用氯气电积流程（文献9），精炼厂于1978年投产。冰镍浸出过程中浸出剂是氯化铁，铁元素被电积槽阳极室内生成的氯气重新氧化。铁离子在溶剂萃取过程中被萃取，反萃后再返回浸出过程。钴也在萃取过程中被萃取。电积厂房有80个电积槽，年产量为13000 t电积镍。3.3 Sulphate electrowinningOutokumpu was the first to introduce, on an industrial scale, the sulphate electrowinning process for nickel using insoluble lead anodes in 1960. Outokumpu had developed a matte treatment process which was based on leaching of ground matte to a sulphate solution. This meant that a compatible electrolysis process with leaching also had to be developed. The nickel smelter and refinery was built at Outokumpus Harjavalta works, where a copper smelter already existed.3.3 硫酸盐电解 奥托昆普公司于1960年首次使用不溶阳极并采用硫酸盐电解流程生产电积镍，并形成工业规模。奥托昆普公司将冰镍磨细后进行浸出并生成硫酸镍溶液。这意味着电积过程和浸出过程要兼容。镍熔炼厂和精炼厂均设在奥托昆普哈贾瓦尔塔厂，而此前这里已经有铜熔炼厂存在。The electrochemical principles of electrowinning in nickel sulphate solutian and the refinery operations at Outokumpu Harjavalta Metals Oy are discussed in more detail in the following chapters. 在后面章节中将详细介绍奥托昆普哈贾瓦尔塔金属公司的硫酸盐溶液电积过程电化学原理和精炼操作流程。4. Characteristics of electrowinning in nickel sulphate solutionIn the electrowinning process, nickel is precipitated from a nickel sulphate solution into metallic form by electric current. The catholic reaction is the reduction of nickel ions on the cathode and the anodic reaction is the oxidation of water on the surface of the lead anode. Electrolysis reactions can be described by the following overall reactions:4、硫酸镍溶液电积过程的特点在电积过程中，硫酸镍溶液中的镍离子通过电流作用沉积为金属镍。阴极反应是镍离子在阴极上还原析出，阳极反应是水在铅阳极上氧化分解。电极反应可用以下方程式表示：阴极反应：Ni2+ + 2e- = Ni0(2)阳极反应：H2O = 2H+ + 1/2O2 + 2e-(3)电极反应：NiSO4 + H2O = Ni0 + H2SO4 + 1/2O2(4)Because nickel is less noble than hydrogen in the electrochemical series and the reduction overpotential for nickel is higher than that for hydrogen, hydrogen evolution is a preferential reaction and a part of the electric current is consumed in the hydrogen evolution reaction:由于在电化学过程中镍元素比氢元素的活性高，镍的还原超电势也要比氢的高，因此在电积过程中析氢反应是首先发生的，一部分的电流消耗在析氢反应上：2H+ + 2e- = H2(5)To minimise the hydrogen evolution, the pH of the solution should be sufficiently high to have a good current efficiency for nickel electrodeposition. Fig. 1 shows the polarisation curves for nickel reduction at different pH values. The curves show that the higher the hydrogen ion concentration, the higher the reduction peak of hydrogen in the potential values between -600 and -650 mV vs. SCE. The reduction peak demonstrates the activity of hydrogen ions. At pH values of 2.5 or higher, hydrogen evolution is low and the main reaction is deposition of nickel. The current efficiency studies at different pH values confirm this phenomenon. At pH 3.0 the current efficiency for nickel is 97% and 94% at pH 2.5, when the current density is 200 A/m2. At pH 2.0 or less the current efficiency decreases drastically. 为减小析氢反应，溶液的pH值必须足够高以保证镍沉积时的电流效率。图1显示了不同pH值下镍还原的极化曲线。曲线表明，氢离子浓度越高，氢的还原峰越高，还原电势位于600650 mV。还原峰表示了氢离子的活性。pH值在2.5或更高时，析氢反应比较小，主要反应是镍离子的沉积。在不同pH值下电流效率的研究同样证明了这一现象。在电流密度为200 A/m2的条件下，当pH值为3.0时，镍沉积电流效率为97%，当pH值为2.5时镍沉积效率为94%。当pH值小于2.0或者更低时，电流效率大幅度下降。Fig. 1 also shows that the polarisation curves shift to more positive values when the pH decreases. The shift is 60 mV per one pH unit, which is a measure of the activity of hydrogen ions according to the Nernst equation.When the pH value is too high, there is a danger that nickel hydroxide will be deposited with nickel. Hydroxide precipitation causes disturbances in the crystal structure of nickel which can be noticed as tension, brittleness or hardening of the deposit.图1同时显示当pH值减小时，极化曲线趋向于更正的值。移动值是每个pH值单位变化60 mV，这也是根据能斯特方程计算出的氢离子的活度变化。当pH值太高时，