Abstract
Incinerated ash with a relatively high Ca content, paper sludge ash, was converted to zeolitic materials with high cation-exchange capacities (CECs) by aging at 80 °C in NaOH solution via step-wise acid leaching with HCl to reduce the ash Ca content. The extraction of Ca, Mg, Si, and Al from the ash into the acid solutions during leaching and the products obtained from the leached ash by reaction with an alkali were examined. The contents of Ca and Mg in the ash were more easily extracted from the ash than those of Si and Al in the initial leaching. The leachant pH decreased with increasing numbers of leaching steps, and the amounts of Si, Al, and Ca extracted from the ash increased as a result of the dissolution of gehlenite (Ca2Al2SiO7), one of the main minerals in the ash. Zeolites A and P were synthesized from the leached ashes, and hydroxysodalite was synthesized from the raw ash. With increasing numbers of leaching steps of the ash, the obtained product contained lower released Ca, whereas the product contained higher released Na and has higher CEC, depending on the zeolite phases in the product. The product with the highest CEC was synthesized from third-leached ash, and its CEC was 1.5 mmol/g, which is about four times higher than that of the raw ash (0.4 mmol/g).
Highlights
In the manufacture of recycled paper, industrial wastes are discharged, and the amounts are increasing annually around the world, e.g., 11 million tons in Europe [1], 5.1 million tons in Japan [2] and 26 million tons in Korea [3]
The amount of anorthite decreased up to the sixth step. These results confirm that gehlenite is more soluble than anorthite, and that only gehlenite crystalline phases in the raw ash can be removed by three steps of acid leaching
Results suggest that quartz, mullite and other phases in leached ashes were mostly unaffected. These results suggest that quartz, mullite and other phasessynthesis, in leached ashes mostly unaffected. These results suggest that anorthite involved zeolite but mostwere of and phases are anorthite is is involved ininzeolite synthesis, but most of gehelenite, gehelenite,talc, talc,quartz, quartz,mullite mullite and phases are anorthite is involved in zeolite synthesis, but most of gehelenite, talc, quartz, mullite and phases are not dependent, which is in good accordance with the results of previous papers [21,22,23]
Summary
In the manufacture of recycled paper, industrial wastes (paper sludge) are discharged, and the amounts are increasing annually around the world, e.g., 11 million tons in Europe [1], 5.1 million tons in Japan [2] and 26 million tons in Korea [3]. The conversion involves the transformation of aluminosilicate, which is a major component of ash, into zeolites by reaction with alkalis Because of their unique porous structures and ion-exchange properties, zeolites, including those synthesized from paper sludge ash, are used in applications such as water purification, gas removal, catalysts and so on [15,16,17,18]. The Ca-P zeolitic product with the simultaneous removal of NH4 + and PO4 3− can be prepared from the Ca obtained from paper sludge ash via acid leaching process and the zeolite-P from leached ash with high Si and Al contents after alkali reaction [24]. Step-wise acid leaching with dilute HCl was applied for the synthesis of zeolitic materials with high CECs from paper sludge ash. The effects of step-wise acid leaching with dilute HCl on the properties of leached ash to enable zeolitic materials with high CECs were investigated to clarify the effective control condition of acid leaching
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
