pH值对烧结砖中重金属释放的影响

采用酸消解实验和NEN 7371浸出实验研究了烧结砖中重金属总量和有效释放量,采用pH-dependence实验研究pH对破碎烧结砖样品中重金属(Cr、Ni、As、Cd和Pb)浸出特性的影响,以及烧结砖样品的酸碱缓冲容量。结果表明,烧结砖中重金属的有效释放量低于总量,释放率从大到小依次为CdAsPbNiCr;烧结砖的酸缓冲容量较小,浸出液pH从7.03降到3.64,消耗了29.33 mmol/kg硝酸,碱缓冲容量较大,pH从7.03升到12.40,共消耗256 mmol/kg氢氧化钠溶液,因此在使用烧结砖的过程中要特别注意环境pH;浸提液的酸碱性是影响烧结砖中重金属浸出的重要参数,在实验研究的pH范围内,不同重金属的浸出规律不同。Cr和As的释放受pH影响较小,而Ni和Cd的浸出量随pH的增大而降低,Pb的浸出量在强酸和强碱条件下均较大,当pH在5.59~9.86的范围内浸出量很低。

Effects of pH on release of heavy metal in sintered brick

The total amounts and availabilities of heavy metals were measured by the means of acid digestion and NEN 7371 experiments. The impacts of pH on the leaching behavior of heavy metals (Cr, Ni, As, Cd and Pb) and the buffer capacity in crushed brick samples were studied by the use of pH-dependence test. The results showed that availabilities of heavy metals are lower than the total amounts in sintered brick. The release rate of heavy metals were different (Cd>As>Pb>Ni>Cr). The alkaline buffer capacity is larger than ANC (acid neutralizing capacity). It took 29.33 mmol/kg Nitric acid to reduce pH from 7.03 to 3.64, and took 256 mmol/kg NaOH solution to increase pH from 7.03 to 12.40. The pH of leaching reagent was important factor impacting the leachability of heavy metals from bricks. In the investigated pH range, different heavy metals had different leaching characteristics. Changes in pH had no significant effect on the release of Cr and As. The leaching amount of Ni and Cd decreased when pH increased. Leaching amount of Pb was larger in strong acid and alkaline condition, but very low in the pH range of 5.59 to 9.86.