从精矿中提取粗金属
地球上发现的所有物质都是由不同的元素组成的。这些元素分布在地球的三个主要部分,即大气、水圈和岩石圈。大多数这些元素的主要来源是岩石圈。元素根据其物理和化学性质大致分为金属和非金属,金属一般是具有光泽光泽(光彩)、延展性和延展性、高导热性和导电性等重要性质的坚硬固体。另一方面,非金属不具备这些特性。它们通常易碎、无光泽,并且导热性和导电性低。元素周期表由金属组成,因为已知大约 80% 的元素是食物。不同的化合物可能包含特定的元素。多种化学原理涉及元素的联合提取和分离。
用于从矿石中分离金属的整个科学技术过程称为冶金。
从浓缩矿石中提取粗金属
加工浓缩矿石以提取金属的过程取决于矿石的性质以及矿石中存在的杂质的性质。这包括氧化和还原反应。浓缩物应转化为适合还原的形式。通常,硫化物矿石在还原之前转化为氧化物,因为氧化物很容易被还原。矿石加工的主要操作包括两个步骤:
- 将浓缩矿石改质为氧化物形式(氧化去电子化)
- 将氧化物改性为金属(还原或电子化)
将浓缩矿石改质为氧化物形式(氧化去电子化)
浓缩矿石是水合氧化物、碳酸盐或硫化物。它可以通过以下两种方法转化为氧化物形式:
- 煅烧:煅烧是将矿石加热到远低于其熔点的过程,无论是在有限的空气供应下还是在没有空气的情况下。在煅烧过程中,会发生以下变化:
- 水分偏转。
- 挥发性杂质被偏转。
- 矿石变得多孔,因此很容易在后期加工。
- 从水合氧化物中除去水。
- 碳酸盐分解成氧化物。
例如,水合氧化物和碳酸盐矿石通常经过煅烧得到氧化物。炉甘石中的锌 (ZnCO₂) 以碳酸锌的形式存在。矿石被煅烧,在没有空气的情况下被强烈加热以将其转化为氧化锌。在煅烧过程中,二氧化碳被排出。铝在其铝土矿中以Al 2 O 3 .2H 2 O 的形式存在。当铝土矿被煅烧时,释放出水蒸气并获得无水氧化铝。从褐铁矿中除去水合水(Fe 2 O 3 .3H 2 O)。
- 焙烧:焙烧是在存在过量空气的情况下将矿石强烈加热到低于金属熔点的温度的过程。这种方法主要用于硫化矿石。由于焙烧,水分和挥发性杂质被去除,矿石被转化为氧化物。
例如,硫、砷和磷的杂质分别作为它们的挥发性氧化物SiO 2 、As、O、P 2 O 5被除去。金属矿石被转化为它们的氧化物。产生的 SO 用于制造 H 2 SO 4 。煅烧和焙烧通常都在反射炉中进行。在这种类型的熔炉中,燃料不会与装料直接接触。火焰从炉顶装料,空气供应可以通过通风口控制。猛烈的火焰与冲锋相撞。沿墙壁有用于生金属和炉渣的出铁口。这种类型的熔炉每天可以熔化大约 10 公斤的炉料。在烘烤过程中,通风口保持打开,而在煅烧过程中,通风口部分或完全关闭。反射炉可用于氧化和还原。
Flux: If the calcined or roasted ore still does not contain impurities of the earthly substance, an additional substance called flux is also added to the ore during reduction. It mixes impurities to form an easily soluble product known as slag. Slag is not soluble in molten metal. Being lightweight, it can be easily skied from molten metal surfaces. That’s why it is necessary to remove the gang. Thus,
Flux is a substance that chemically combines with gangue (earth impurities) that may still be present in calcined or roasted ore to form an easily soluble material called slag.
Types of fluxes
There are two types of fluxes- basic flux and acidic flux. The choice of flux depends on the nature of the impurities present in the reaction. for example,
- Basic Flux: If the ore contains acidic impurities such as SiO₂, P₂O, etc., then basic fluxes like lime (Cao), limestone (CaCO3), magnesite hematite (Fe2O3 etc. are used.
- Acid Flux: If the basic impurities are present in the ore such as CaO, FeO, MgCO3, etc., then acidic fluxes like send(SiO2) or borax (Na2B4O7), are used.
将氧化物改性为金属(还原或电子化)
Metal oxides are usually reduced to free metals using a suitable reducing agent such as carbon, carbon monoxide, or another metal. The reduction process involves electron gain or electronification.
The process of extraction of metal by heating a metal oxide with a suitable reducing agent is called thermal reduction pyrometallurgy.
一些金属很容易还原(在低温下还原),而另一些则很难还原(即在高温下还原)。然而,可以注意到还原总是需要加热。可以根据后面讨论的基本热力学概念来理解适合作为给定金属氧化物的还原剂的元素的选择以及还原顺利进行的最佳温度。根据氧化物和金属的性质,可以通过以下还原剂提取金属:
- 用 C 或 CO 还原:在 Fe、Cu、Pb、Sn、Zn、Mg、Co 等的冶金中。
- 用 Na、Al、Mg 或氢还原:在 Mn、Cr、Ti、Mo、W 等的冶金中。
- 水煤气(CO,H₂)还原:在镍的冶金中。
- Pb、Hg 2 Cu等冶金中的自还原或自还原。
示例问题
问题 1:金属在自然界中不以硝酸盐的形式存在。为什么?
回答:
Nitrates of all metals are soluble in water. Hence, if metal nitrates are extant in the Earth’s crust, these will lightly and gradually be washed into the ocean by rainwater. Therefore, metals usually do not occur in the form of nitrates.
问题2:石墨常用作阳极,但S到Zn金刚石不常用。给理由。
回答:
Graphite is a good conductor of electricity due to the presence of free electrons within its layers. But no free electrons are present and hence, it is a poor conductor of electricity. Therefore, diamond is not used as a mode.
问题 3:为什么在还原之前焙烧氧化物中的硫化物矿石是有利的?
回答:
The standard free energy of formation (ΔfG0) of most of the sulphides is larger than those of CS2 and H2S. Therefore, these sulfides are more stable than sulfides containing carbon or hydrogen. Therefore, neither carbon nor hydrogen can convert metal sulfide to metal. Conversely, the standard free energy oxides have much lower immersion than 80, and the conversion of metal sulfides to metal oxides is thermodynamics. Therefore, it is common practice to roast the sulfide in oxide ore before reduction.
问题4:熔剂在冶金过程中的作用是什么?
回答:
Flux is used to make the melted mass more conductive. The flux combines with the impurities to form an easily pliable product called a separation.
问题 5:金属如何被提炼成半导体?所用方法的原理是什么?
回答:
Semiconductor metals are manufactured by the field purification method which is based on the principle that impurities are more soluble in the melt than in the solid-state of the metals.
问题 6:给出气相纯化的两个要求。
回答:
- The metal should form a volatile compound with the available reagent.
- The volatile compound must be volatile and easily decomposable so that recovery is easy.