Chromium removal from chromium gypsum through microwave hydrothermal crystal phase regulation.

Chromium gypsum (CG) is a common hazardous waste formed in chromium salt or electroplating industries. The trapped or lattice-doped CrO42- in gypsum crystals are difficult to be reduced or removed by traditional methods, which will be re-oxidized or slowly released during long-term hypaethral storage. In this study, microwave hydrothermal treatment was applied to remove chromium in CG. Under optimal conditions (solid-liquid ratio of 1:5, 0.1 M sulfuric acid as liquid media, and 110 °C), over 99% of the chromium in CG can be removed within 10 min. XRD spectra indicated that 59.8% gypsum was transformed to from dihydrate gypsum to hemihydrate gypsum. The toxicity leaching test shows that chromium in CG is 377.0 mg/L before detoxification and 0.55 mg/L after detoxification, which proves that chromium in CG lattice can be efficiently removed. This work enables to significantly advance the dehydration phase transformation process of gypsum and release the heavy metal impurities within it more quickly and provides new possibilities to treat similar solid waste containing gypsum or minerals with hydration water.

Construction of heterostructured NiFe2O4-C nanorods by transition metal recycling from simulated electroplating sludge leaching solution for high performance lithium ion batteries.

NiFe2O4 has been regarded as one of the promising candidates for lithium-ion battery (LIB) anode materials due to its high theoretical specific capacity. However, the large volume expansion and pulverization of NiFe2O4 during the charge/discharge process result in severe capacity fading. Herein, heterostructured NiFe2O4-C nanorods have been successfully fabricated by recovering transition metals from simulated electroplating sludge leaching solution. The constructed NiFe2O4-C heterointerface plays a vital role in accommodating volume change, stabilizing the reaction products and providing rapid electron and Li+ ion transportation ability, resulting in a high and stable Li+ accommodation performance. The fabricated NiFe2O4-C nanorods demonstrate a high specific capacity (889.9 mA h g-1 at 100 mA g-1), impressive rate capability (861.5, 704.5, 651.4, 579.6 and 502.1 mA h g-1 at 0.2, 0.6, 1.0, 2.0 and 5.0 A g-1) and cycling stability (650.2 mA h g-1 at 2 A g-1 after 500 cycles). This work exemplifies a facile and effective approach for the fabrication of high performance LIB electrode materials by recycling metals from electroplating sludge in an application-oriented manner.

Targeted conversion of Ni in electroplating sludge to nickel ferrite nanomaterial with stable lithium storage performance.

The recovery of heavy metals from industrial solid waste is of great significance for simultaneously alleviating heavy metal pollution and recycling valuable metal resources. However, the complex compositions of the multiple metallic electroplating waste severely limit the selective recovery of metal resources such as nickel. In this study, a kind of nickel-laden electroplating sludge was taken as an example and the Ni in it was targetedly converted into highly valuable NiFe2O4 (nickel ferrite) nanomaterials via a regulator assisted hydrothermal acid-washing strategy, eventually leading to selective extraction of Ni and Ca from the sludge. Sodium carbonate was the best regulator for the formation of NiFe2O4, and under the optimal conditions, the extraction rates of Ni and Ca are 96.70 % and 99.66 %, respectively. The as-prepared NiFe2O4 nanoparticles exhibited stable electrochemical Li-storage performances, such as a reversible capacity of approximate 316.94 mA h/g at 0.5 A/g and a long cycle life exceeding 100 cycles, with nearly no capacity decay. This work provides a facile and sustainable approach for targeted conversion of heavy metals in industrial solid waste to high-valuable functional materials and selective recovery of heavy metals from multi-metal solid wastes.