Is aluminum hydroxide precipitation?

從鋁土礦生產(chǎn)氧化鋁的拜耳法經(jīng)濃堿高溫浸出得到鋁酸鈉濃溶液，從中沉淀析出氫氧化鋁是其極其重要的一個步驟。拜耳溶液中的Al呈[Al（OH）4]－配離子形式存在，它不穩(wěn)定，經(jīng)水解析出氫氧化鋁沉淀，其反應(yīng)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:

沉淀的氫氧化鋁可能呈晶態(tài)，也可能為膠體狀，其形態(tài)取決于沉淀的條件，包括母液組成、溫度和有無晶種等。典型的拜耳溶液含Al2O380kg∕m3左右，Na2O∕Al2O3比（指摩爾比，下同）在1.5～2.5之間，簡單的稀釋或降溫只能得到膠狀氫氧化鋁，難于分離和洗滌。實踐上加晶種幫助結(jié)晶分離，習(xí)慣上稱為“種分”，做法是將前一循環(huán)中新生成的5～150μm氫氧化鋁晶體作為晶種，大大過量地帶入新的結(jié)晶循環(huán)中，降溫并緩緩攪拌大約4d，得到粗粒的氫氧化鋁晶體。

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.

沉淀的初始階段，結(jié)晶速度與晶種表面積成正比。有效的攪拌是必要的，否則細小的晶種容易聚結(jié)而降低結(jié)晶速度。在25～35℃下攪拌36h可結(jié)晶出約70%的鋁。某些組分如溶解的鐵、釩和鈣鹽對結(jié)晶有負面影響，因而通常稱為抑制劑或中毒劑。這些抑制劑應(yīng)限制在規(guī)定的低水平以保證必要的結(jié)晶速度。沉淀的氫氧化鋁沉降槽底，經(jīng)過濾、洗滌后煅燒成氧化鋁產(chǎn)品。母液蒸發(fā)濃縮密度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.

氫氧化鋁在不同領(lǐng)域的應(yīng)用

Application of aluminum hydroxide in different fields

氫氧化鋁，不含鹵素，不產(chǎn)生腐蝕性產(chǎn)物，而且也比較低，這些都是它的使用特點，除此之外它受歡迎的原因就是它的應(yīng)用特別廣泛，在很多領(lǐng)域中都發(fā)揮著重要作用。

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、不飽和粱浦中的應(yīng)用

1. Application of unsaturated sorghum

在玻瑞纖維增強的不飽和聚醋澆注塑料中(如各種高壓或低壓電器開關(guān))，氮載化鋁是作為填料使用，使塑料制品具有阻撼性、消煙性以及抗電弧性，氫氧化鋁還用于玻璃鋼層壓制體，如玻瑞鋼瓦、管子、貯槽等，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、環(huán)乳樹脂中的應(yīng)用

2. Application of ring emulsion resin

在環(huán)氧樹脂中，有的阻嫩效果，用量為40%-60%載指數(shù)比未經(jīng)填充的環(huán)氧樹脂高一倍, 同時還增強了抗電弧性和抗弧跡性。經(jīng)氦暇化鋁墳充的環(huán)氧樹脂在側(cè)作變壓器、絕緣器材、開關(guān)裝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、乳膠和拈合荊中的應(yīng)用

3. Application of latex and twisted wattle

地毯襯墊的乳膠橡皮和梭酸化膠乳枯合劑是氫氧化鋁的早市場，這方面的消耗今還居地位。它在預(yù)涂層、粘合劑和泡沫材料中還代替阻燃能力很小的碳酸鈣和白土作具有阻燃性的填充料。一般是100份膠乳加20-150份粒徑3~ 205m的氮氧化鋁，而在粘合劑中加入75-250份，估計，今后膠乳襯墊仍是氮氧化鋁較大的消耗者。

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、聚氛乙烯中的應(yīng)用

4. Application of polyatmosphere in ethylene

氫氧化鋁在熱塑性塑料中研究多的領(lǐng)域便是聚氛乙烯。它可以取代碳酸鈣填料非常容易摻合到增塑的PVC中。有兩種方法能達到高標(biāo)準(zhǔn)的阻燃性:其一是氫氧化鋁和麟酸醋類增塑荊并用，另一種方法是將氫氧化鋁和翻酸鋅并用，這些祝方已應(yīng)用于PVC的電線電纜料中，在硬聚抓乙烯中加入氫氧化鋁主要是起消煙作用。

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子熱童性塑樸中的應(yīng)用氨氧化鋁已用于阻燃裝飾用鈣塑板中,并取得了良好的效果但在這些熱塑性塑料中，氧化鋁單獨使用時的添加量一定要達到60%6以 上才能顯示出一定的阻徽性、而此時塑料的抗沖擊強度會嚴重受到影響。所以到目前為止它在這些熱塑性塑料中的應(yīng)用仍是繼續(xù)研究的課題。

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、合成探膠中的應(yīng)用

6. Application of synthetic gel

在T苯膠、抓丁膠這一類合成橡膠中氫氧化鋁是一種很好的阻嫩劑，所得到的制品氧指數(shù)達50,垂直和水平燃燒性優(yōu)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.

氫氧化鋁能夠在不同領(lǐng)域中發(fā)揮作用的前提就是質(zhì)量的考驗，所以在選購產(chǎn)品時一定要注意質(zhì)量的考察，否則可能不能使其更好的發(fā)揮作用。

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.