【作者】 黄赟；

【导师】 林宗寿；

【作者基本信息】 武汉理工大学 ， 材料学， 2010， 博士

【摘要】 磷石膏是磷化工企业湿法生产磷酸的工业副产品,每1吨磷酸将产生5吨磷石膏。随着我国磷化工业的快速发展,每年副产磷石膏已经超过4000万吨,累计堆积磷石膏超过2亿吨。由于种种原因,目前我国磷石膏的资源化利用率不足10%,剩余部分作为固体废弃物采用堆积或者填埋等方式处理,磷石膏堆积不但占用了大量土地,而且对周围环境造成严重污染,加快对磷石膏的资源化利用已经刻不容缓。本文通过大量试验,以未经煅烧处理的磷石膏为主要原料,通过添加钢铁工业的高炉水淬矿渣和少量碱性激发剂,开发出一种新型低能耗的水硬性胶凝材料——磷石膏基水泥,并通过组分设计和制备工艺优化对提高磷石膏水泥的性能进行了研究。结果表明：使用45%的磷石膏与35%-45%的矿渣复合,添加10%钢渣或者4%的硅酸盐水泥作为碱性激发剂,可以制备出28d抗压强度超过40MPa的水硬性胶凝材料。尽管该水泥凝结慢、早强低,但在水中养护强度能不断增长。在钢渣激发的磷石膏基水泥中添加1%的NaOH,能显著缩短水泥的凝结时间和提高早期强度,用超细粉磨的硅酸盐水泥做碱性激发剂,磷石膏基水泥的3d抗压强度超过12MPa,接近于32.5复合硅酸盐水泥。通过XRD、SEM等对磷石膏基水泥的水化产物、水化机理、水化过程及微观结构的发展进行了研究。结果表明：磷石膏基水泥的水化产物是C-S-H凝胶和钙矾石,磷石膏在水化过程中一部分参与水化形成水化产物钙矾石,剩余部分被水化产物所包裹起集料填充作用。磷石膏基水泥水化时,矿渣在碱性激发下溶解,并与溶解在液相中的石膏形成水化产物钙矾石和C-S-H凝胶,钙矾石和C-S-H凝胶交织在一起填充空隙,硬化浆体结构逐渐密实,强度不断发展。早期水化形成的钙矾石,起到填充空隙作用,和C-S-H凝胶一起构成硬化浆体的骨架,有利于促进水泥凝结和提高早期强度。当硬化浆体的致密性达到一定程度后,如果还形成大量结晶粗大的钙矾石,水化产物中结晶相过多,并不利于浆体结构致密度的提高,严重时还会因钙矾石的结晶压力使浆体结构产生破坏,造成水泥的后期强度降低甚至膨胀开裂。由于磷石膏基水泥中石膏是过剩的,通过控制磷石膏基水泥中碱性激发剂的适当掺量,可避免膨胀性钙矾石所造成的破坏。通过试验对磷石膏基水泥的长期强度、体积稳定性、抗碳化性能、耐水性、抗硫酸盐性能等耐久性进行了研究,结果表明：1、磷石膏基水泥在水中长期养护时,强度能不断发展,增加到一定程度时趋于稳定,其强度发展时间和所能达到的最终强度随着矿渣掺量的增加而增加。2、钢渣激发磷石膏基水泥在水中养护时,具有微膨胀性,膨胀到一定程度后趋于稳定,膨胀量的大小随着水泥强度的提高而减少,在空气中养护时,与普通硅酸盐水泥一样,体积出现收缩,收缩量约为普通硅酸盐水泥的一半。硅酸盐水泥激发磷石膏基水泥在水中养护时,水泥掺量少的试样出现了收缩,水泥掺量多的试样具微膨胀性,膨胀量低于钢渣激发磷石膏基水泥。3、磷石膏基水泥的抗碳化性能劣于普通硅酸盐水泥,在碳化箱中人工碳化28d后,磷石膏基水泥的抗压强度为未碳化时的65%-84%,降低幅度与未碳化时的强度有关,强度越高的试样,碳化后降低的比例越少。碳化时碳酸与磷石膏基水泥的水化产物C-S-H凝胶和钙矾石反应,形成了方解石和石膏,使浆体结构疏松化,是磷石膏基水泥碳化后强度降低的主要原因。4、磷石膏基水泥水化产物中含有大量剩余石膏,早期水化结构还未发展致密时,浸泡在水中有部分石膏溶解,但随着水化进行,石膏被水化产物钙矾石和C-S-H凝胶包裹紧密,溶解越来越慢最终停止,因此具有很好的耐水性。5、磷石膏基水泥具有很好的抗硫酸盐性能,这是因为其水化过程中一直是在石膏过剩的条件下进行,水化产物的碱度较低,硬化浆体的结构致密,硫酸盐侵蚀介质难以与水泥的水化产物发生化学反应形成石膏或钙矾石。更多还原

【Abstract】 Phosphogypsum (PG) is a byproduct of manufacturing phosphate acid by wet process in fertilizer industry. Five tons PG is generated for every 1000 kg phosphate acid produced. The annual production of PG is more than 40 million tons with the rapid development of China’s phosphate industry, and total accumulation of PG is more than 200 million tons in China. Due to various reasons, less than 10% PG is reused and the rest is deposited as solid waste. The deposited PG not only occupies a lot of land, but also causes serious environment pollution. It is urgent to expedite the utilization of PG.In this study, a new type of low energy consumption hydraulic binder phosphogypsum-based-cement (PBC) had been developed by mainly utilizing PG and ground granulated blast-furnace slag (GGBFS) with small addition of alkaline activator, and experiments of component design and production process optimization were conducted to improve the property of PBC. The results show that, the 28d compressive strength of PBC made with 45%PG,35-40%GGBFS and 10%steel salg or 4%portland cement as alkaline activator was over 40 MPa when cured in water. Although the setting time of PBC was slow and the early strength was low, but its strength increased continuously cured in water. The early strength was increased and the setting time was shortened by adding 1%NaOH in steel slag activated PBC. The 3d strength of PBC was up to 12 MPa by using super fine ground portland cement as alkaline activator which is close to that of 32.5 portland blended cement.The hydration products, hydration mechanism and process, and microstructure development of PBC were studied by XRD and SEM analyses. The main hydration products of PBC were C-S-H gel and ettringite. Partial PG reacts with GGBGS and alkaline activator to form ettringite, the rest PG was enclosed by the hydration products to act as filler. At the hydration of PBC, GGBFS was dissolved into pore solution by alkaline activation, which then reacted with gypsum to form hydration products ettringite and C-S-H gel. Ettringite and C-S-H gel mingled together to fill the porous space. As a result, the microstructure of hardened paste became increasingly denser, and the strength of PBC developed continuously. Ettringite formed during early hydration filled the porous space, which contributed together with C-S-H gel to shorten the setting time and to improve the early strength of cement. If large amount of ettringite formed after the density of the hardened paste reached to a certain degree, the excessive crystalline phase from hydration was harmful to density improvement of the microstructure; it may cause damage to microstructure due to the ettringite crystallization pressure, which resulted in the deterioration of strength development or even expansive cracks. Because the gypsum was excess in PBC, the damage of expansive ettringite could be avoided by controlling the dosage of alkaline activator.The durability properties of PBC, including long term strength, volume stability, carbonation resistance, water resistance and sulfate resistance were also studied. The results show that:1. The strength of PBC increased continuously when cured in water and stabilized at about one year. The final strength of PBC was higher at higher dosage of GGBFS.2. When cured in water, steel slag activated PBC showed small expansion at beginning, and its volume was stable after a certain amount of expansion. The amount of expansion was decreased with increase of PBC strength. When cured in air, the PBC shrank like portland cement, but its shrinkage was about half of that of portland cement. Portland cement activated PBC shrank if cement dosage less than 3% and swell if cement dosage more than 3% when cured in water.3. Carbonation resistance of PBC was inferior to that of portland cement. After carbonated for 28d in carbonation test box, the compressive strength of PBC was retained 65-84%. The strength decrease was related to the strength of the specimens before carbonation, the higher the strength before carbonation the less the strength decreased. Carbonate acid reacted with hydration products C-S-H gel and ettringite of PBC and formed calcite and gypsum, which made the PBC microstructure less cohesive and was the main reason for strength loss after carbonation.4. The hydration products of PBC contained large amount of residual gypsum. At early hydration, the microstructure was not dense enough and when immersed in water some gypsum was dissolved. But as hydration continued, gypsum was wrapped by hydration products of C-S-H gel and ettringite, dissolution became more difficult and finally stopped. As a result, PBC showed very good water resistance.5. PBC was also resistant to sulphate because its hydration process was under the condition of saturation of gypsum, the alkalinity of hydration products was low, and its microstructure was dense. Consequently, it was difficult for sulphate erosion media to react with the hydration products of PBC and form ettringite and gypsum.更多还原