Abstract
In this work, the design of a monolithic softener obtained by geopolymer gel conversion is proposed. The softener used consists in a geopolymeric macroporous matrix functionalized by the co-crystallization of zeolite A and X in mixture. The dual nature of the proposed material promotes a softening process based on the synergistic effect of cation exchange and alkaline precipitation. A softening capacity of 90% and 54% for Ca2+ and Mg2+ respectively was attained in 24 h. In fact, the softener reported a Cation Exchange Capacity (CEC) value of 4.43 meq g−1. Technical features such as density, porosity and mechanical resistance were also measured. The use of this monolithic softener can improve performance and sustainability of hardness removal from tap water, reducing the production of sludge and adding the possibility to partially regenerate or reuse it.
Highlights
The total concentration of magnesium and calcium in water, known as water hardness, represents a great problem for all the industrial processes which use water for steam generation, such as textile, paper, dying industry
Among the chemical precipitation methods, lime softening, involving the use of specific compounds that help in precipitation of C a2+ and Mg2+ ions by removing water hardness, is still known as a cost-effective treatment in some a pplications[16]
To estimate the removal efficiency RE of calcium and magnesium, the maximum adsorption was calculated according to the following e quation[31]: RE = Ci − Cf · V (2) m where Ci [mg L−1] is the initial concentration of cation in the tap water, Cf [mg L−1] the concentration of cation at the end of the kinetic test, m [g] the sample mass and V [L] the volume of solution
Summary
The total concentration of magnesium and calcium in water, known as water hardness, represents a great problem for all the industrial processes which use water for steam generation, such as textile, paper, dying industry. A complete K → Na reverse exchange was performed on the same sample and under the same operating conditions (using a 1 M NaCl solution), obtaining the total amount of exchanged K+ cations. To estimate the removal efficiency RE of calcium and magnesium, the maximum adsorption was calculated according to the following e quation[31]: RE = Ci − Cf · V (2) m where Ci [mg L−1] is the initial concentration of cation in the tap water, Cf [mg L−1] the concentration of cation at the end of the kinetic test, m [g] the sample mass and V [L] the volume of solution.
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