Sintered-clay waste (arising from the crushing of red and blue bricks), as the main constituent of urban construction waste, has a porous structure and water purification components: the fixed adsorbents (SiO2, MgCa(CO3)2) and the effective purification substances (sodium aluminum silicate, potassium aluminum silicate), which provide a new adsorbent for the purification of high-hardness arsenic-containing water. Analysis of the components of sintered clay and filtered sintered clay showed that adsorption, complexation, and chemical reactions were the main purification mechanisms of high-hardness arsenic-containing water. The pore-specific surface area of the large-particle sintered-clay filter media was smaller than that of their small-particle counterparts. The experimental results showed that the process of total hardness softening included three stages: the accelerated stage, the decelerated stage, and the stable stage; the arsenic removal process consisted of three stages: the decelerated stage, the accelerated stage, and the stable stage. Both the effective purification duration of the total hardness and arsenic was 40–60 > 20–40 ≈ 10–20 mesh; the removal rates were 40–60 > 20–40 > 10–20 mesh at each purification stage, and the optimal particle size of the sintered-clay filter media was 20–40 mesh. After filtration, the amounts of components SiO2 and MgCa(CO3)2 increased in the sintered-clay media; SiAs2 and Pb28As12S46 also appeared. The precipitates and the strong-adsorbent flocculation substances Al(OH)3 were produced during the reaction between Ca2+, Mg2+, and silicates and aluminates in the sintered clay. The ions Ca2+, Mg2+, and arsenic were further removed during Al(OH)3 redissolution and surface group M–OH complexation with Ca2+ and Mg2+. Both the confidence ranges of the total hardness and arsenic were narrow, and the confidence range of total hardness softening showed a greater change in the early stage than in the later stage; the trend for arsenic ran contrary. The average correlation coefficients of the total hardness and arsenic adsorption models were, respectively, significant at 0.9410 and 0.9625, and both consistencies of experimental adsorption capacities with their theoretical counterparts were greater in the middle stages than in the end stages. The hardness removal rate was 69.36%, and that of arsenic was 53.45%, both higher than those achieved by existing adsorption filters for purifying high-hardness arsenic-containing water.
Qinghao Xin (Thu,) studied this question.