氢氧化铝是沉淀吗？
Is aluminum hydroxide precipitation?
从铝土矿生产氧化铝的拜耳法经浓碱高温浸出得到铝酸钠浓溶液，从中沉淀析出氢氧化铝是其极其重要的一个步骤。拜耳溶液中的Al呈[Al（OH）4]－配离子形式存在，它不稳定，经水解析出氢氧化铝沉淀，其反应如下：
The Bayer process of producing alumina from bauxite is leaching with concentrated alkali at high temperature to obtain concentrated sodium aluminate solution, from which precipitation of aluminum hydroxide is an extremely important step. Al in Bayer solution exists in the form of [al (OH) 4] – coordination ion, which is unstable. Aluminum hydroxide precipitation is resolved by water, and its reaction is as follows:

沉淀的氢氧化铝可能呈晶态，也可能为胶体状，其形态取决于沉淀的条件，包括母液组成、温度和有无晶种等。典型的拜耳溶液含Al2O380kg∕m3左右，Na2O∕Al2O3比（指摩尔比，下同）在1.5～2.5之间，简单的稀释或降温只能得到胶状氢氧化铝，难于分离和洗涤。实践上加晶种帮助结晶分离，习惯上称为“种分”，做法是将前一循环中新生成的5～150μm氢氧化铝晶体作为晶种，大大过量地带入新的结晶循环中，降温并缓缓搅拌大约4d，得到粗粒的氢氧化铝晶体。
The precipitated aluminum hydroxide may be crystalline or colloidal, and its morphology depends on the precipitation conditions, including mother liquor composition, temperature and the presence or absence of crystal seeds. The typical Bayer solution contains about 380kg / m3 of Al2O3, and the Na2O / Al2O3 ratio (refers to the molar ratio, the same below) is between 1.5 and 2.5. Simple dilution or cooling can only obtain colloidal aluminum hydroxide, which is difficult to separate and wash. In practice, crystal seed is added to help crystallization separation, which is traditionally called "seed separation". The method is to add 5 ~ 150 newly generated in the previous cycle μ M aluminum hydroxide crystal as crystal seed is brought into the new crystallization cycle in large excess, cooled and stirred slowly for about 4 days to obtain coarse-grained aluminum hydroxide crystal.
沉淀的初始阶段，结晶速度与晶种表面积成正比。有效的搅拌是必要的，否则细小的晶种容易聚结而降低结晶速度。在25～35℃下搅拌36h可结晶出约70%的铝。某些组分如溶解的铁、钒和钙盐对结晶有负面影响，因而通常称为抑制剂或中毒剂。这些抑制剂应限制在规定的低水平以保证必要的结晶速度。沉淀的氢氧化铝沉降至槽底，经过滤、洗涤后煅烧成氧化铝产品。母液蒸发浓缩至密度1.45kg·m－3后返回浸出。
In the initial stage of precipitation, the crystallization rate is directly proportional to the surface area of crystal seed. Effective stirring is necessary, otherwise fine crystal seeds are easy to coalesce and reduce the crystallization speed. About 70% aluminum can be crystallized by stirring at 25 ~ 35 ℃ for 36 hours. Some components, such as dissolved iron, vanadium and calcium salts, have a negative effect on crystallization, so they are usually called inhibitors or medium poisons. These inhibitors shall be limited to the specified low level to ensure the necessary crystallization rate. The precipitated aluminum hydroxide settles to the bottom of the tank and is calcined into alumina products after filtration and washing. The mother liquor is evaporated and concentrated to a density of 1.45kg · M-3 and then returned for leaching.
氢氧化铝在不同领域的应用
Application of aluminum hydroxide in different fields
氢氧化铝无毒，不含卤素，不产生腐蚀性产物，而且价格也比较低，这些都是它的使用特点，除此之外它受欢迎的原因就是它的应用特别广泛，在很多领域中都发挥着重要作用。
Aluminum hydroxide is non-toxic, halogen-free, does not produce corrosive products, and the price is relatively low. These are its use characteristics. In addition, the reason why it is popular is that it is widely used and plays an important role in many fields.
1、不饱和粱浦中的应用
1. Application of unsaturated sorghum
在玻瑞纤维增强的不饱和聚醋浇注塑料中(如各种高压或低压电器开关)，氮载化铝是作为填料使用，使塑料制品具有阻撼性、消烟性以及抗电弧性，氢氧化铝还用于玻璃钢层压制体，如玻瑞钢瓦、管子、贮槽等，具有很好的阻徽效果。
Aluminum nitride is used as filler in the unsaturated polyacetic cast plastics reinforced by Borui fiber (such as various high-voltage or low-voltage electrical switches), so that the plastic products have shock resistance, smoke elimination and arc resistance. Aluminum hydroxide is also used in FRP laminates, such as Borui steel tiles, pipes, storage tanks, etc., which has a good resistance effect.
2、环乳树脂中的应用
2. Application of ring emulsion resin
在环氧树脂中，有特效的阻嫩效果，用量为40%-60%载指数比未经填充的环氧树脂高一倍, 同时还增强了抗电弧性和抗弧迹性。经氦暇化铝坟充的环氧树脂在侧作变压器、绝缘器材、开关装里等方面前途是十分光明的。
In the epoxy resin, it has a special anti tenderness effect. The dosage is 40% – 60%, and the load index is twice as high as that of the Unfilled epoxy resin. At the same time, it also enhances the arc resistance and arc trace resistance. The epoxy resin filled with helium aluminum has a bright future in side transformer, insulation equipment, switchgear and so on.
3、乳胶和拈合荆中的应用
3. Application of latex and twisted wattle
地毯衬垫的乳胶橡皮和梭酸化胶乳枯合剂是氢氧化铝的早市场，这方面的消耗至今还居领先地位。它在预涂层、粘合剂和泡沫材料中还代替阻燃能力很小的碳酸钙和白土作具有阻燃性的填充料。一般是100份胶乳加20-150份粒径3~ 205m的氮氧化铝，而在粘合剂中加入75-250份，估计，今后胶乳衬垫仍是氮氧化铝较大的消耗者。
Latex rubber and shuttle acidified latex drying agent of carpet liner are the early market of aluminum hydroxide, and the consumption in this regard is still in the leading position. It is also used in precoating, adhesive and foam materials instead of calcium carbonate and white clay with low flame retardancy as flame retardant filler. Generally, 100 parts of latex are added with 20-150 parts of nitrogen alumina with particle size of 3 ~ 205m, while 75-250 parts are added to the adhesive. It is estimated that the latex liner will still be a large consumer of nitrogen alumina in the future.
4、聚氛乙烯中的应用
4. Application of polyatmosphere in ethylene
氢氧化铝在热塑性塑料中研究最多的领域便是聚氛乙烯。它可以取代碳酸钙填料非常容易掺合到增塑的PVC中。有两种方法能达到高标准的阻燃性:其一是氢氧化铝和麟酸醋类增塑荆并用，另一种方法是将氢氧化铝和翻酸锌并用，这些祝方已应用于PVC的电线电缆料中，在硬聚抓乙烯中加入氢氧化铝主要是起消烟作用。
Polyethylene atmosphere is the most studied field of aluminum hydroxide in thermoplastics. It can replace calcium carbonate filler and can be easily mixed into plasticized PVC. There are two methods to achieve high standards of flame retardancy: one is the combination of aluminum hydroxide and Lin acid vinegar plasticizers, and the other is the combination of aluminum hydroxide and zinc titanate. These methods have been applied to PVC wire and cable materials, and the addition of aluminum hydroxide to hard polyethylene is mainly used to eliminate smoke.
5、聚乙蜂、粱苯L蜂,ABS子热童性塑朴中的应用氨氧化铝已用于阻燃装饰用钙塑板中,并取得了良好的效果但在这些热塑性塑料中，氧化铝单独使用时的添加量一定要达到60%6以 上才能显示出一定的阻徽性、而此时塑料的抗冲击强度会严重受到影响。所以到目前为止它在这些热塑性塑料中的应用仍是继续研究的课题。
5. Application of polyethylene bee, Liang benzene l bee and ABS hot child plastic Pu ammonia alumina has been used in flame retardant decorative calcium plastic board and achieved good results. However, in these thermoplastics, the addition amount of alumina must reach more than 60% 6 when used alone to show a certain resistance, and the impact strength of the plastic will be seriously affected at this time. So far, its application in these thermoplastics is still a subject of continuous research.
6、合成探胶中的应用
6. Application of synthetic gel
在T苯胶、抓丁胶这一类合成橡胶中氢氧化铝是一种很好的阻嫩剂，所得到的制品氧指数达50,垂直和水平燃烧性优良。
Aluminum hydroxide is a good tenderness inhibitor in synthetic rubber such as t benzene gum and polybutadiene rubber. The oxygen index of the product is up to 50 and the vertical and horizontal flammability is excellent.
氢氧化铝能够在不同领域中发挥作用的前提就是质量的考验，所以在选购产品时一定要注意质量的考察，否则可能不能使其更好的发挥作用。
The premise that aluminum hydroxide can play a role in different fields is the test of quality, so we must pay attention to the investigation of quality when purchasing products, otherwise it may not play a better role.