The use of fly ash can produce a good quality lightweight clay refractory material - lightweight refractory insulation bricks. Its raw materials can be used fly ash, burnt stone, hard soil, soft soil and sawdust for batching, and can also be used for batching with fly ash, purple wood knots, mountain soil and sawdust. First of all, all kinds of raw materials are crushed separately, screened according to the particle size requirements and stored separately. Fly ash requires the removal of impurities, and it is best to use hollow beads after sorting. The ratio and particle size requirements are listed in Table 1.利用粉煤灰可以生產(chǎn)出質(zhì)量較好的輕質(zhì)黏土耐火材料——輕質(zhì)耐火保溫磚。其原料可用粉煤灰、燒石、硬質(zhì)土、軟質(zhì)土及木屑進(jìn)行配料，也可用粉煤灰、紫木節(jié)、山皮土及木屑進(jìn)行配料。首先將各種原料分別進(jìn)行粉碎，按照粒度要求進(jìn)行篩分并分別存放。粉煤灰要求除去雜質(zhì)，最好選用分選后的空心微珠。配比和粒度要求如表1所列。

Fly ash lightweight refractory insulation brick is characterized by high thermal insulation efficiency, high refractoriness, small thermal conductivity, can reduce the thickness of the furnace wall, shorten the firing time, reduce fuel consumption, improve thermal efficiency, low cost, has been widely used in electric power, steel, machinery, military, chemical, petroleum, shipping and other industries.粉煤灰輕質(zhì)耐火保溫磚的特點(diǎn)是保溫效率高，耐火度高，熱導(dǎo)率小，能減輕爐墻厚度，縮短燒成時(shí)間，降低燃料消耗，提高熱效率，成本低，現(xiàn)已被廣泛應(yīng)用于電力、鋼鐵、機(jī)械、軍工、化工、石油、航運(yùn)等工業(yè)方面。The extraction of alumina from fly ash by limestone sintering process has been studied by people abroad and has been put into industrial production. China has also carried out experimental research in this regard. The process flow is shown in Figure 1. The main process is clinker firing, self-pulverization and dissolution, desiliconization, carbon separation and calcination. The basic principles of each process are as follows:

.熟料燒成

主要是使粉煤灰中的Al2O3與石灰石中的CaO化合生成易溶于碳酸鈉溶液的5CaO·3Al2O3，另一方面又使粉煤灰中的SiO2與石灰石中的CaO生成不溶性的2CaO·SiO2。這便為溶出Al2O3創(chuàng)造了必要的條件。

2.熟料自粉化

當(dāng)熟料冷卻時(shí)，在約650℃溫度下，C2S由β相轉(zhuǎn)變?yōu)棣孟?，因體積膨脹發(fā)生熟料的粉碎現(xiàn)象，自粉化后幾乎全部能通過200號篩孔。

3.溶出

用碳酸鈉溶液溶出粉化料，其中的鋁酸鈣與堿反應(yīng)生成鋁酸鈉進(jìn)入溶液，而生成的碳酸鈣和硅酸二鈣留在渣中，便達(dá)到鋁和硅、鈣分離的目的。其反應(yīng)式可以下式表示：

5CaO·3Al2O+5Na2CO3+2H2O→5CaCO3+6NaAlO2+4NaOH

4.脫硅

為保證產(chǎn)品氧化鋁純度，需進(jìn)一步除去溶出粗液中的二氧化硅。

5.碳分

以CO2與鋁酸鈉溶液反應(yīng)，得到氫氧化鋁，并使生成的Na2CO3循環(huán)使用。

6.鍛燒

氧化鋁可作電解鋁的原料、人造寶石原料、陶瓷釉原料、高級耐火材料等。提取氧化鋁后的殘?jiān)?硅鈣渣作為水泥原料具有反應(yīng)活性高、燒成溫度低、利于節(jié)能、水泥標(biāo)號高且性能穩(wěn)定、配料簡單、吃灰量大等特點(diǎn)，是生產(chǎn)水泥的一種優(yōu)質(zhì)原料。

從粉煤灰中提取氧化鋁和硅鈣渣制水泥將會成為綜合利用粉煤灰資源，消除環(huán)境污染的有效手段之一。Clinker firing

It mainly combines Al2O3 in fly ash with CaO in limestone to form 5CaO·3Al2O3 which is soluble in sodium carbonate solution, and on the other hand, SiO2 in fly ash and CaO in limestone to form insoluble 2CaO· SiO2。 This creates the necessary conditions for the dissolution of Al2O3.

2. Clinker self-pulverization

When the clinker is cooled, at a temperature of about 650 °C, the C2S changes from the β phase to the γ phase, and the clinker is crushed due to volume expansion, and almost all of it can pass through the No. 200 sieve hole after self-pulverization.

3. Dissolution

The pulverized material is dissolved with sodium carbonate solution, in which calcium aluminate reacts with alkali to form sodium aluminate into the solution, and the generated calcium carbonate and dicalcium silicate remain in the slag to achieve the purpose of separation of aluminum, silicon and calcium. The reaction can be expressed as follows:

5CaO·3Al2O+5Na2CO3+2H2O→5CaCO3+6NaAlO2+4NaOH

4. Desiliconization

In order to ensure the purity of the alumina of the product, the silica in the dissolved crude solution needs to be further removed.

5. Carbon content

CO2 is reacted with sodium aluminate solution to obtain aluminum hydroxide, and the generated Na2CO3 is recycled.

6. Calcining

Alumina can be used as raw materials for electrolytic aluminum, artificial gemstones, ceramic glaze raw materials, high-grade refractory materials, etc. As a cement raw material, the residue after alumina extraction-calcium silica slag has the characteristics of high reactivity, low firing temperature, energy saving, high cement grade and stable performance, simple batching, and large ash consumption, and is a high-quality raw material for the production of cement.

The extraction of alumina and calcium silica slag from fly ash to make cement will become one of the effective means to comprehensively utilize fly ash resources and eliminate environmental pollution.