Recycling of Ni(II)-citrate complexes using precipitation in alkaline solutions

Reaction of aqueous Cu-Citrate with MnO2 birnessite: characterization of Mn dissolution, oxidation products and surface interactions

Citric acid, a widespread soil rhizosphere plant/microbe carboxylic acid exudate can easily form chelates with heavy metals, increasing their availability in the environment. When Cu(II) from algal control in water bodies or reservoirs and fungicides, such as the Bordeaux mixture, and citrate interact, solubilization through chelation is a possible outcome. Manganese (hydr)oxides represent a significant portion of the subsurface environment and can affect the fate and transport of chemical species through adsorption and oxidation. This study explores the possible interaction between MnO2 and Cu-Citrate under ambient oxic conditions. The calculated Mn(II) dissolution rates during the initial 1h of reaction followed the series Cu(II)>Cu-Citrate 1:0.5>Cu-Citrate 1:1(oxic)>Citrate>Cu-Citrate 1:1(Anoxic), reinforcing the central role of (complexed or un-complexed) Cu(II) during the initial surface-coordination instead of following the s-shaped auto-catalytic curves of Mn(II) dissolution in citrate solution. The use of capillary electrophoresis allowed the detection of an intermediate Cu(II)Acetonedicarboxylate complex and the oxidation products acetonedicarboxylate, acetoacetate, acetone and acetic acid. The mass balance analysis of Cu-Citrate 1:1 suggests the partial adsorption of Cu-Citrate(ads) and catalytic degradation of acetonedicarboxylate through a MnO2-Cu surface sorbed complex. Lastly, XPS analysis confirmed the MnO2 surface Cu(II) reduction along with an outer-hydration layer at the MnO2 interface, where electron transfer and aquo ligand exchange may lead to the oxidation of Cu-Citrate.

Preparation and characterization of 5-sulphosalicylic acid doped tetraethoxysilane composite ion-exchange material by sol-gel method

In this manuscript, we report the preparation and characterization of sulphosalicylic doped tetraethoxysilane (SATEOS), composite material by sol-gel method as a new ion exchanger for the removal of Ni(II) from aqueous solution. The fine granular material was prepared by acid catalyzed condensation polymerization through sol-gel mechanism in the presence of cationic surfactant. The material has an ion exchange capacity of 0.64 mequiv./g(dry) for sodium ions, 0.60 mequiv./g(dry) for potassium ions, 1.84 mequiv./g(dry) for magnesium ions, 1.08 mequiv./g(dry) for calcium ions and 1.36 mequiv./g(dry) for strontium ions. Its X-ray diffraction studies suggest that it is crystalline in nature. The material has been characterized by SEM, IR, TGA and DTG so as to identify the various functional groups and ion exchange sites present in this material. Quantum chemical computations at DFT/B3LYP/6-311G (d,p) level on model systems were performed to substantiate the structural conclusions based ion instrumental techniques. Investigations into the elution behaviour, ion exchange reversibility and distribution capacities of this material towards certain environmentally hazardous metal ions are also performed. The material shows good chemical stability towards acidic conditions and exhibits fast elution of exchangeable H(+) ions under neutral conditions. This material shows remarkable selectivity for Ni(II) and on the basis of its Kd value (4×10(2) in 0.01M HClO4) some binary separations of Ni(II) from other metal ions are performed.

Simultaneous biodegradation of Ni-citrate complexes and removal of nickel from solutions by Pseudomonas alcaliphila

The objective of this study was to study the simultaneous biodegradation of Ni-citrate complexes and removal of Ni from solutions by Pseudomonas alcaliphila. Adding excess citrate to 1:1 Ni-citrate complexes promoted the degradation of the complexes and removal of Ni. The alkaline pH generated by the metabolism of excess citrate caused partial dissociation of citrate from the Ni-citrate complexes, allowing degradation, and the released Ni was removed through bioaccumulation and precipitation. Addition of Fe(3+) enhanced the degradation of Ni-citrate complexes and removal of Ni from solutions. The displacement of Ni from recalcitrant Ni-citrate complexes by Fe(3+) and subsequent biodegradation of the degradable Fe(III)-citrate complex resulted in complete metabolism of citrate. The almost complete removal of Ni (>98%) can be attributed to the combination of coprecipitation with Fe(3+), bioaccumulation and precipitation. P. alcaliphila potentially could be applied in the treatment of effluent containing Ni-citrate complexes.

Recovery and reuse of Ni(II) from rinsewater of electroplating industries

Discharge of nickel compounds, which may occur in both liquid and solid phases, can cause severe environmental problems. In this work, 'point of source' treatment strategy is followed and reduced the nickel content of rinsewater to about less than 1 mg L(-1) by ion-exchange method using a packed column involving batch recirculation mode of operation and to recovered Ni(II) content by desorption. The treated water could be recycled for rinsing operation. The nickel from resin is first precipitated as nickel hydroxide to synthesize positive active material and that was used in Nickel/Metal hydride cell. The performances in terms of electrochemical utilization of nickel hydroxide, specific capacity as a function of discharge current density and cycle life were examined and the nickel hydroxide electrode with 5% CaCO(3) addition, having 200 mAh g(-1) specific capacity, could be subjected to charge/discharge cycles at C/5 rate for more than 200 cycles without the capacity fading.