Hydroxide precipitation is the most widely used heavy metal wastewater treatment method. However, the metal hydroxide sludge produced must be treated concurrently. In this paper, an integrated treatment procedure, which modifies hydroxide precipitation with oxidation treatment and sulfide precipitation, is proposed to sequentially precipitate Fe, Cu, and Zn from wastewater for metal recovery. An industrial wastewater specimen containing Cu ($290\pm 6.25\mathrm{mg}/\mathrm{L}$ ), Fe ($\mathrm{2,092}\pm 12.3\mathrm{mg}/\mathrm{L}$ ), and Zn ($\mathrm{4,648}\pm 15.4\mathrm{mg}/\mathrm{L}$ ) was used. First, hydroxide precipitation using lime was applied to study the precipitation characteristics of Cu, Fe, and Zn, following which ${\mathrm{H}}_2{\mathrm{O}}_2$ oxidation treatment and NaHS sulfide precipitation were conducted and integrated with hydroxide precipitation to selectively precipitate Cu, Fe, and Zn from the wastewater specimen. The Fe, Cu, and Zn were sequentially removed from the wastewater by introducing 0.1% (v/v) ${\mathrm{H}}_2{\mathrm{O}}_2$ , altering the pH of the wastewater to pH 3.5–4.0 using lime, adding $1\mathrm{g}/\mathrm{L}$ NaHS, and subsequently altering the pH to 9.0. The Fe, Cu, and Zn were subsequently separated as individual precipitates with recoveries of $99.8\pm 0.1$ , $94.0\pm 0.3$ , and $96.1\pm 0.7\%$ , respectively, which can facilitate metal recovery and render sludge disposal unnecessary.

Cement is the most widely used construction material in the world. However, its manufacture is high energy consumption and high carbon emission owing to the high temperature calcination process. Geopolymer is an ideal alternative material for cement because it has a similar structure and performance to cement. In addition, it can be synthesized at room temperature and thus has the advantages of energy saving and carbon emission reduction. Sewage sludge (SS) can be used as raw material for geopolymer synthesis. However, the high organic matter content in SS lowers the mechanical strength of geopolymer. Although the organic matter in SS can be removed by incineration at high temperature, this consumes energy and emits carbon dioxide, which diminishes the advantages of geopolymer. In this study, the Fenton method was applied for the removal of organic matter in SS at room temperature. The parameters of the Fenton method, including the dosages of hydrogen peroxide (H₂O₂) and Fe²⁺ reagent (FeSO₄·7H₂O), reaction time, and initial pH value, were investigated. The results indicated that 83.7% of the organic matter in SS could be removed at room temperature by using 5.15 M H₂O₂ and 5.15 mM FeSO₄·7H₂O at pH 7, which suggested the possibility of sewage sludge reclamation through geopolymer synthesis as an alternative material for cement toward sustainability.

Abrasive–glass polishing waste is generated from the polishing process of glass components by using cerium oxide abrasive, which contains the cerium oxide abrasive and the polished glass. This study attempted to recover the cerium oxide abrasive from the abrasive–glass polishing waste through removing the polished glass by alkaline roasting using sodium hydroxide (NaOH) followed by water leaching. The experimental results indicated that the polished glass in the abrasive–glass polishing waste could be fully removed under the optimal alkaline roasting and water leaching conditions of roasting temperature of 450 °C, mass ratio of polishing waste to NaOH of 1:1, roasting time of 30 min, leaching pH of 3, leaching temperature of 25 °C, and liquid–solid ratio of 25 mL/g. The characteristics including elemental composition, particle size distribution, mineralogical phases, and morphology of the recovered cerium oxide abrasive obtained under the optimal conditions were similar to those of the original unused one, which was suitable to be reused for polishing again.

The IC lead frame is an essential component in semiconductor packaging, primarily composed of a nickel (Ni)–copper (Cu) alloy in which Ni is electroplated onto a Cu substrate. In this study, synergistic solvent extraction using a binary extractant containing LIX984N and Cyanex302, followed by two-stage selective stripping using sulfuric acid (H₂SO₄) and nitric acid (HNO₃) as the stripping agent, was employed to separate and recover Cu and Ni from the leachate of an IC lead frame. The results indicated that under the optimal conditions of synergistic solvent extraction with an extraction pH value of 1, an extractant concentration of 0.015 M LIX984N + 0.0375 M Cyanex302, an extraction aqueous/organic (A/O) ratio of 1:1, and an extraction time of 5 min, the extraction efficiencies for Cu and Ni were 99.8% and 1.17%, respectively. The distribution ratios were D_Cu 999 and D_Ni 0.012, resulting in a separation factor of 83,250. In addition, the separation factor was much higher than that of using individual extractant of LIX984N (6208.3) or Cyanex302 (22,185.2). Subsequently, under optimal first-stage stripping conditions, using 0.05 M H₂SO₄ at a stripping organic/aqueous (O/A) ratio of 1:1, and with a stripping time of 3 min, a stripping efficiency of 99.9% for Ni was achieved. Next, under optimal second-stage stripping conditions, using 5 M HNO₃ at a stripping O/A ratio of 2:1, and with a striping time of 3 min, a stripping efficiency of 99.9% for Cu was achieved. Finally, sodium hydroxide (NaOH) was added to the respective stripping solutions to precipitate Ni and Cu ions, followed by calcination treatment for the precipitates to obtain NiO and CuO, respectively. The purity of the former was 99.74% and that of the latter was 99.82%. The results demonstrate that synergistic solvent extraction using a binary extractant containing LIX984N and Cyanex302 can almost entirely extract Cu in the leachate of an IC lead frame at a lower extraction pH and a lower extractant concentration, thus reducing the co-extraction of Ni. In addition, less co-extracted Ni in the organic phase can be selectively stripped using dilute H₂SO₄, thus reducing the co-stripping of Cu. Hence, the effective separation and recovery of Cu and Ni in IC lead frame leachate can be achieved, which contributes to improving the sustainability of natural resources.

In a world with a growing human population, resources are becoming increasingly scarce. To ensure food supply, fertilizers are often used to accelerate growth when planting agricultural products. Sewage sludge (SS), containing as high as 10–15 wt% Phosphorus (P), can be synthesized into liquid fertilizer. P species in SS can generally be classified into four types: inorganic phosphorus (IP), organic phosphorus (OP), nonapatite inorganic phosphorus (NAIP), and apatite phosphorus (AP). However, OP is not leached out by wet chemical methods and NAIP is not bioavailable. This study investigated the P-form conversion (OP and NAIP to AP) in SS by adding 8 wt% CaO at 300 °C. SS through pretreatment can easily leach out P when combined with organic acid. The content of heavy metals is in accordance with fertilizer regulations in a leaching solution. The solution was mixed with potassium and ammonia compounds to synthesize a liquid fertilizer. To ensure the safe and efficient use of liquid fertilizer and undertake an analysis of heavy metals, an aquatic organisms (D. magna) toxicity test, and the growth of plants test were both used. The liquid fertilizer can be demonstrated to accelerate the growth of plants while not causing the death of D. magna in short time, as the liquid fertilizer has enough nutrients to help the D. magna to survive.

In this paper, a novel procedure is proposed for comprehensively recovering zinc fluoride (ZnF₂), manganese fluorides [MnF_{x(x = 2, 3)}], manganese dioxide (MnO₂), and carbon powder from the electrode powder of spent alkaline batteries. Firstly, hydrofluoric acid (HF) leaching is conducted on the electrode powder of spent alkaline batteries. Secondly, potassium permanganate (KMnO₄) is introduced into the leachate to selectively precipitate manganese (Mn) ions to recover MnO₂. Subsequently, the water content in the leachate is evaporated to recover ZnF₂. Finally, the leaching residue is leached again by using HF, after which the water content in the leachate is evaporated to recover MnF_x. The results indicated that under optimal conditions of a HF concentration of 4 M, a leaching time of 15 min, and a liquid–solid ratio of 5 mL/g, the optimal leaching selectivity for Zn and Mn was achieved and the leaching efficiencies of Zn and Mn were 97.83% and 39.94%, respectively. When KMnO₄ with a dosage (KMnO₄/Mn ion molar ratio) of 0.5:1 was added to the leachate, MnO₂ with a grade of 91.68% and a Mn recovery of 39.07% was obtained. In addition, ZnF₂ with a grade of 97.98% and a Zn recovery of 96.15% was also obtained after removing the water content from the leachate via evaporation. Under the optimal conditions of a HF concentration of 2 M, a leaching time of 15 min, and a liquid–solid ratio of 10 mL/g for the leaching residue, followed by removing the water content in the leachate via evaporation, MnF_x with a grade of 94.20% and a Mn recovery of 59.46%, was obtained. The residue of the releaching process was carbon powder. The effectiveness of the proposed recovery procedure was confirmed.