Instituto de metalurgia, Universidad Autónoma de San Luis Potosí, Av. Sierra Leona 550 C.P. 78210, San Luis Potosí, Mexico; Guangdong Provincial Key Laboratory of Environmental Health and Land Resource, Zhaoqing University, Zhaoqing 526061, China E-mail:
Instituto de metalurgia, Universidad Autónoma de San Luis Potosí, Av. Sierra Leona 550 C.P. 78210, San Luis Potosí, Mexico.
Water Sci Technol. 2021 Nov;84(9):2304-2317. doi: 10.2166/wst.2021.449.
Activated carbon has been widely used to remove hazardous Cr(VI); however, the impact of CrO precipitate on gradually declining removal ability as pH increases has received little attention. Herein, to investigate the effect of CrO, SEM-EDX (scanning electron microscope-energy dispersive X-ray analysis) coupling elements mapping of chromium-loaded powdered activated carbon (PAC) revealed that a chromium layer was formed on the PAC exterior after being treated with Cr(VI) at pH 7. XPS (X-ray photoelectron spectroscopy) study confirmed that 69.93% and 39.91% CrO precipitated on the PAC surface at pH 7 and pH 3, respectively, corresponding to 17.77 mg/g and 20 mg/g removal capacity. Exhausted PAC had a removal efficiency of 92.43% after CrO being washed by HSO solution, which was much higher than the removal efficiency of 51.27 % after NaOH washing. This further verified that the intrinsically developed CrO precipitate on PAC under neutral conditions limited the durability of PAC as an adsorbent. Consecutive elution assessments confirmed that adsorption and reduction ability both declined as pH increased. Raman spectroscopy and C 1s spectra of materials demonstrated two distinct Cr(VI) removal mechanisms under pH 3 and pH 7. In conclusion, the exhausted AC after Cr(VI) adsorption can be rejuvenated after the surface coated CrO is washed by the acid solution, which can expand the longevity of AC and recover Cr(III).
活性炭已广泛用于去除有害的六价铬；然而，对于随着 pH 值升高而逐渐下降的去除能力，CrO 沉淀的影响却很少受到关注。在此，为了研究 CrO 的影响，通过对负载铬的粉末活性炭（PAC）进行 SEM-EDX（扫描电子显微镜-能量色散 X 射线分析）耦合元素映射，揭示了在 pH 值为 7 时用 Cr(VI)处理后，PAC 外表面形成了一层铬层。XPS（X 射线光电子能谱）研究证实，在 pH 值为 7 和 pH 值为 3 时，PAC 表面分别有 69.93%和 39.91%的 CrO 沉淀，对应的去除容量分别为 17.77 mg/g 和 20 mg/g。用 HSO 溶液洗涤 CrO 后的耗尽的 PAC 的去除效率为 92.43%，远高于用 NaOH 洗涤后的去除效率 51.27%。这进一步证明了在中性条件下 PAC 上固有地开发的 CrO 沉淀限制了 PAC 作为吸附剂的耐久性。连续洗脱评估证实，随着 pH 值的升高，吸附和还原能力均下降。材料的拉曼光谱和 C 1s 谱表明，在 pH 值为 3 和 pH 值为 7 时，存在两种不同的 Cr(VI)去除机制。总之，吸附 Cr(VI)后的废 AC 可以用酸溶液洗涤表面覆盖的 CrO 后再生，可以延长 AC 的寿命并回收 Cr(III)。
