Shamkhi and Hussein 2021 — Low-cost adsorbents for Pb, Ni, and Zn removal from wastewater (JEASD conference review)
Open-access conference-proceedings review from the Environmental Engineering Department at Mustansiriyah University (Baghdad) surveying ~13 prior adsorption studies that used agricultural- or industrial-waste materials (tea fibre, fava beans, rice husk, hazelnut shell, apple pomace, orange peel xanthate, red mud, etc.) to remove Pb(II), Ni(II), and Zn(II) from aqueous solutions. No primary sampling, no PRISMA, no quality assessment, no quantitative synthesis. The paper’s scope is wastewater treatment engineering, not food or supply-chain contamination; relevance to the Heavy Metal Index is limited to (a) the regulatory drinking-water limits the authors cite in passing for Pb, Ni, and Zn, and (b) a leads list of food-derived materials that have been studied as Pb/Ni/Zn sorbents (apple pomace, fava beans, rice husk, orange peel, tea fibre, hazelnut shell). Evidence tier C; cite as a leads document, not as direct evidence for occurrence values.
Key numbers
Regulatory drinking-water and supplement limits cited by the review (not primary; verify before applying)
The review states the following limits without specific edition or year citations beyond “as per environmental regulations” or “as stated by WHO” / “as stated by EPA”:
- Pb — “maximum quantity of lead permitted in water sources is 0.1 mg/L, as per environmental regulations” (p. 3-89). This value disagrees with the current WHO 2022 Guidelines for Drinking-water Quality provisional value of 0.01 mg/L for lead and with US EPA’s MCLG of zero / action level of 0.015 mg/L. Re-verify before any HMTc use.
- Zn — “World health organization (WHO) limits the amount of zinc in drinking water to 5.0 parts per million (ppm)” (p. 3-89). The current WHO guideline does not establish a formal health-based guideline for zinc; 5 mg/L is noted as a provisional/secondary value above which taste objections arise. Verify against WHO 4th edition (2022) before citing.
- Ni — “the permissible permitted content of nickel in drinking water is 0.1 mg/L” (p. 3-90, attributed to “environmental protection authorities”). The current WHO drinking-water guideline value for nickel is 0.07 mg/L (provisional).
Industrial-effluent characterization cited by the review
- Ni in metal-plating wastewater — “varies from 6 to 12 mg/L” (p. 3-89, attributed to refs [32–34]).
Adsorbent-performance figures the review reports as standalone statements (cited values from primary papers, not the review’s own measurements)
The values below are the review’s restatement of figures from the primary references; sample mass, pH, contact time, isotherm fit, and removal efficiency are all reported in the review’s narrative without uncertainty estimates or replication structure. Verify against the original papers before any quantitative use.
- Singanan [ref 41] — Tridax procumbens leaves for Pb(II) removal: optimal pH 4.5; 180-min equilibrium contact time; 2.5 g dose; maximum lead removal efficiency 95 %; Langmuir and Freundlich isotherms both fit.
- Chand and Pakade [ref 42] — apple pomace for Pb(II): optimal conditions 0.8 g dose, pH 4.0, 80-min contact time; q_max 16.39 mg/g (r² = 0.985); pseudo-second-order kinetics.
- Abbas et al. [ref 43] — baker’s yeast biomass for Pb(II): Langmuir model best fit (R² = 0.9987 for Pb(II)); pseudo-second-order kinetics (R² = 0.979).
- Shrestha et al. [ref 44] — Lapsi seed stone activated carbon for Ni(II): optimal pH 5; sorption capacities 28.258 mg/g (H₂SO₄-treated) and 69.49 mg/g (1:1 H₂SO₄/HNO₃-treated). The “28.25 8” appearing in the review’s text is treated here as a typographic separation of “28.258 mg/g”; cross-check against the primary paper to confirm.
- Demirbaş et al. [ref 45] — hazelnut shell activated carbon for Ni(II): 180-min equilibrium contact time; Langmuir isotherm strongest association.
- Malakahmad et al. [ref 46] — waste black tea for Ni(II) and Zn(II): pH 5; 250-min contact time; 20 g/L adsorbent dose; q_max 90.91 mg Ni/g and 166.67 mg Zn/g; Langmuir and Freundlich both fit.
- Etorki et al. [ref 47] — fava beans for Pb(II) and Zn(II): particle diameter 250–500 µm; Pb removal efficiency 100 %; Zn removal efficiency 36.86 %; Langmuir model fit.
- Kumar and Acharya [ref 48] — NCRH (sodium-carbonate-treated rice husk) for Pb(II): removal efficiency 98 %; pseudo-second-order kinetics.
- Liang et al. [ref 49] — orange peel xanthate for Pb(II), Zn(II), and Ni(II): q_max 218.34, 49.85, and 15.45 mg/g respectively; pseudo-second-order kinetics; Langmuir isotherm best fit.
- Ghorbani et al. [ref 50] — red mud (bauxite mining waste) for Pb adsorption: stated as “effective” without quantitative removal efficiency reported in the review.
Methods (brief)
Narrative review of secondary literature on low-cost adsorbents for Pb(II), Ni(II), and Zn(II) removal from aqueous solutions. No PRISMA, no inclusion/exclusion criteria, no quality assessment, no formal data extraction, no quantitative synthesis. Fifty references cited (the references list runs to ref 50, with the in-text discussion section drawing on refs 38–50). The review structure is: (1) introduction to heavy-metal pollution sources; (2) impacts of heavy metals; (3) source and toxicity of Pb, Ni, and Zn on human health; (4) catalog of adsorbent studies; (5) conclusions. No author-derived analytical work. Two authors, single institution, single submission round (conference proceedings; the 2nd Online Scientific Conference for Graduate Engineering Students, June 2021), light peer review. Open access under CC BY via the journal’s hosted instance at jeasd.uomustansiriyah.edu.iq.
Limitations
Conference proceedings, C-tier. The paper has noticeable English-language and copy-editing issues (e.g., “Astrasia” for Adansonia-like plant naming, “28.25 8” reading as a numeric typographic separation, “heliopathy” appearing where “erythropoiesis” or “haematopoiesis” is the likely intended term). The regulatory drinking-water limits the authors restate disagree with the current WHO and US EPA values for Pb (0.1 mg/L stated vs. 0.01 mg/L current WHO provisional / 0.015 mg/L EPA action level) and Ni (0.1 mg/L stated vs. 0.07 mg/L current WHO provisional). Adsorbent-performance figures are restatements of primary-paper claims without uncertainty estimates, replication structure, or instrument metadata; q_max and removal-efficiency values should not be cited from this review without consulting the underlying papers. The catalogue of adsorbent studies overlaps substantially with adjacent review papers from the same author network and offers no original synthesis.
Implications
This source has minimal direct value for the Heavy Metal Index. The wiki’s scope is heavy-metals occurrence in food and personal-care supply chains; this paper is a wastewater-treatment engineering review. It is retained as a leads document for two narrow purposes:
Regulatory leads: the WHO drinking-water context for Pb, Ni, and Zn (5 mg/L Zn aesthetic threshold; nickel 0.07 mg/L provisional; lead 0.01 mg/L provisional) is sometimes referenced when the wiki contrasts drinking-water guidelines with food-matrix limits. This source can be cited as a starting point for that context, but the actual WHO guideline values must come from the WHO 4th-edition document, not from this review’s restatement.
Material-science leads: several food-derived materials studied here as Pb/Ni/Zn sorbents — apple pomace, fava beans, rice husk, orange peel, hazelnut shell, waste black tea — are themselves food-system commodities that appear elsewhere in the HMI corpus as contamination subjects. The adsorption studies cited by this review are not direct evidence about contamination in those ingredients, but they document baseline adsorption affinities between those plant matrices and these three metals, which can be useful background for understanding metal uptake during cultivation, processing, and packaging.
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