Chromium Ion Adsorption in Acidic Wastewater

Overview

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specific surface area of 2165 m2 /g. A Cr(VI) removal efficiency exceeding 99.6% could be
100 mA. The diffraction patterns were recorded over a 2θ range of 2◦ –80◦ at a scanning rate
Germany) with a scanning range of 4000–400 cm−1 .
was set at 1250 W, with a sample flush time of 20 s, a stable time of 20 s, and a reading
initial Cr(VI) concentration (100–500 mg/L), pH (1–7), and temperature (25–45 ◦ C). The
In the recycling tests conducted, the Cr(VI) concentration was fixed at 100 mg/L, with
EDS analysis in Table 1 shows significant differences in the C/O mass ratio among
HCM2.5 (80.93 wt% C). Consequently, HCM2.5 has the highest oxygen content of 19.07 wt%.
Table 2. The pore structure characteristics of hollow carbon microspheres (HCM, HCM5 and HCM2.5 )
As shown in Table 2, it can be seen that after KOH activation, the BET specific sur-
BET characterization (Table 2), which collectively confirm the structural regulation effect
Figure 6. Adsorption capacities of HCM, HCM2.5 , HCM5 for 50 ppm Cr(VI) at different pH.
tested pH range, achieving 49.8 mg/g at pH 3, which is significantly higher than those
area (2165.0 m2 /g) and abundant oxygen-containing functional groups (19.07 wt%), which
The adsorption capacity reaches the maximum at pH = 3, with a removal rate of 99.6%. Zeta
Figure 10. (a) For the adsorption experiment with an initial Cr(VI) concentration of 50 ppm at pH
of the dosage of HCM2.5 at 300 ppm Cr(VI) (pH = 3) on the adsorption capacity and removal rate.
HCM2.5 in 300 ppm Cr(VI) solution (pH = 3) with varying dosages. The removal efficiency
capacity decreases accordingly. The optimal dosage of HCM2.5 is 5 g/L in 300 ppm Cr(VI)
solution, achieving the highest removal efficiency of 73.08%.
conducted and the results are shown in Figure 11, Tables 3 and 4. The initial concentration
of Cr(VI) was set at 150 mg/L, with the adsorbent dosage of 1 g/L and the adsorption
Table 4. Parameters of intraparticle diffusion fitting model for adsorption of Cr(VI).
Furthermore, as can be seen from Table 3 and Figure 11b,c, the maximum adsorption
pH = 3, a Cr(VI) concentration varying from 100 to 500 mg/L, and an adsorption duration
the endothermic nature of the adsorption process. Meanwhile, the 1/n values of all temper-
HCM2.5 were calculated, and the results are presented in Table 6. ∆S and ∆H were de-
temperature range of 288.15 K to 308.15 K, the calculated ∆H = 13.78 kJ/mol (∆H > 0)
Table 7 compares the thermodynamic parameters of HCM2.5 with other Cr(VI) adsor-
qmax value of 235.7 mg/g (as shown in Table 8).
Table 8. Performance comparison of similar materials.
initial Cr(VI) concentrations (50, 100, and 200 ppm) at a fixed pH of 3. The results revealed
(50 ppm), the inhibitory effect of coexisting anions (Cl− , NO3 − , and SO4 2− ) was negligible,
tration increased to 100 ppm and further to 200 ppm, the competitive adsorption effect of
different pH values at an initial concentration of 50 ppm, (b) effects of coexisting anions on the Cr(VI)
than 93% of its initial capacity with only slight overall attenuation. Statistical analysis of
decreased from 2.231 cm3 /g to 1.916 cm3 /g, corresponding to reductions of 8.8% and 14.1%,
Table 9. The pore structure characteristics of hollow carbon microspheres (HCM2.5 , HCM2.5 (Cycle
EDS results (Table 10) reveal that the C/O atomic ratio of HCM2.5 exhibits only a
cific surface area of 2165 m2 /g. A Cr(VI) removal efficiency exceeding 99.6% could be
achieved in 50 ppm acidic solution, with excellent performance at pH 2–5, demonstrating

Methods (brief)

Waltham, MA, USA), with samples sputter-coated with gold and an accelerating voltage
Inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis: The
Agilent 7800 ICP-OES spectrometer (Agilent Technologies Inc., Santa Clara, CA, USA). The
was set at 1250 W, with a sample flush time of 20 s, a stable time of 20 s, and a reading
and the residual Cr(VI) concentration was quantified by ICP-OES (33). The investigation
the three samples, which follows the order: HCM (86.80 wt% C) > HCM5 (82.62 wt% C) >
of 2.28 nm. In the medium-to-high relative pressure region, both activated samples show
crystalline diffraction peaks are observed in all samples, and only broad diffuse humps
appear, indicating that all materials are of amorphous structure. All samples show a broad
A comparison of the samples with different activation degrees shows the following.
both samples are deconvoluted into four components: C-C/C-H (~284.8 eV) (purple peak),
among the three samples, and it also maintains a moderate proportion of C=O groups,
HCM5 was investigated, and the results are shown in Figure 6. All three samples exhibit
HCM2.5 samples after one and two adsorption–desorption cycles show no significant

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The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised