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.利用粉煤灰可以生产出质量较好的轻质黏土耐火材料——轻质耐火保温砖。其原料可用粉煤灰、烧石、硬质土、软质土及木屑进行配料，也可用粉煤灰、紫木节、山皮土及木屑进行配料。首先将各种原料分别进行粉碎，按照粒度要求进行筛分并分别存放。粉煤灰要求除去杂质，最好选用分选后的空心微珠。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.粉煤灰轻质耐火保温砖的特点是保温效率高，耐火度高，热导率小，能减轻炉墙厚度，缩短烧成时间，降低燃料消耗，提高热效率，成本低，现已被广泛应用于电力、钢铁、机械、军工、化工、石油、航运等工业方面。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:
.熟料烧成
主要是使粉煤灰中的Al2O3与石灰石中的CaO化合生成易溶于碳酸钠溶液的5CaO·3Al2O3，另一方面又使粉煤灰中的SiO2与石灰石中的CaO生成不溶性的2CaO·SiO2。这便为溶出Al2O3创造了必要的条件。
2.熟料自粉化
当熟料冷却时，在约650℃温度下，C2S由β相转变为γ相，因体积膨胀发生熟料的粉碎现象，自粉化后几乎全部能通过200号筛孔。
3.溶出
用碳酸钠溶液溶出粉化料，其中的铝酸钙与碱反应生成铝酸钠进入溶液，而生成的碳酸钙和硅酸二钙留在渣中，便达到铝和硅、钙分离的目的。其反应式可以下式表示：
5CaO·3Al2O+5Na2CO3+2H2O→5CaCO3+6NaAlO2+4NaOH
4.脱硅
为保证产品氧化铝纯度，需进一步除去溶出粗液中的二氧化硅。
5.碳分
以CO2与铝酸钠溶液反应，得到氢氧化铝，并使生成的Na2CO3循环使用。
6.锻烧
氧化铝可作电解铝的原料、人造宝石原料、陶瓷釉原料、高级耐火材料等。提取氧化铝后的残渣-硅钙渣作为水泥原料具有反应活性高、烧成温度低、利于节能、水泥标号高且性能稳定、配料简单、吃灰量大等特点，是生产水泥的一种优质原料。
从粉煤灰中提取氧化铝和硅钙渣制水泥将会成为综合利用粉煤灰资源，消除环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.
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