Preparation of an Aluminum and Iron‐Based Coagulant From Fly Ash for Industrial Wastewater Treatment

Fly ash was investigated to produce a composite coagulant containing aluminum (Al) and iron (Fe) salts through the calcination and leaching processes. The extraction of Al and Fe oxides from fly ash demonstrated similar results for HCl and H2SO4 leaching. Besides, the calcination pretreatment of fly ash (without any additive) was found to be less effective in extraction. However, the conversion efficiencies of Al and Fe were affected greatly by calcination pretreatment with addition of Na2CO3, and leaching conditions of ratio of solution to fly ash (L/S) and H+ concentration. The maximum concentrations of Al and Fe solubilized from fly ash were 0.21 and 0.04 mol/L, respectively, which were attained by calcination pretreatment using an optimal mass ratio (ca. 1:16.7) of Na2CO3 to fly ash at 805°C. These concentrations correspond to conversion efficiencies of 31.2% for Fe and 18.3% for Al in the fly ash. The slurry was filtrated to obtain a solution containing Al- and Fe- sulfates and silicates. The Al/Fe/Si mole ratio indicated the feasibility of further production of inorganic polymer coagulant. The produced coagulant was determined to be effective for treating soybean wastewater and dairy wastewater in terms of COD and SS removal.

研究了通过煅烧和浸出工艺利用粉煤灰生产含铝（Al）和铁（Fe）盐的复合混凝剂。从粉煤灰中提取铝和铁的氧化物时，盐酸和硫酸浸出的结果相似。此外，发现粉煤灰的煅烧预处理（无任何添加剂）在提取方面效果较差。然而，添加碳酸钠的煅烧预处理以及液固比（L/S）和氢离子浓度等浸出条件对铝和铁的转化效率有很大影响。从粉煤灰中溶解的铝和铁的最大浓度分别为0.21摩尔/升和0.04摩尔/升，这是在805°C下使用碳酸钠与粉煤灰的最佳质量比（约1:16.7）进行煅烧预处理时达到的。这些浓度对应的粉煤灰中铁的转化效率为31.2%，铝的转化效率为18.3%。将浆液过滤以获得含有硫酸铝、硫酸铁和硅酸盐的溶液。铝/铁/硅的摩尔比表明了进一步生产无机高分子混凝剂的可行性。经测定，所生产的混凝剂在去除化学需氧量（COD）和悬浮物（SS）方面对处理大豆废水和乳制品废水是有效的。