Zinc oxide (ZnO) nanorods were fabricated through hydrothermal route and employed for the adsorption of Cr(VI) ions from aqueous medium. Zinc nitrate hexahydrate (Zn(NO3)2.6H2O) was used as a zinc precursor and Triton-x 100 was used as a capping agent. As synthesized ZnO nanorods were characterized by UV-visible spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-Ray spectroscopy (EDX) techniques. The adsorption affecting parameters were investigated for maximum adsorption of Cr(VI) onto ZnO nanorods. The adsorption kinetics, isotherms, and thermodynamics were applied for adsorption mechanism evaluation. Maximum adsorption of Cr(VI) ions (250 mg/g) was achieved using 0.055 g/L ZnO dose at pH 2.0 for the contact time of 30 min. Pseudo-second-order kinetic model and Langmuir isotherm explained well the Cr(VI) adsorption onto ZnO nanorods. The Cr(VI) adsorption onto ZnO was spontaneous and endothermic in nature. In view of promising adsorption efficiency, ZnO nanorods could possibly be used for Cr(VI) ions removal from wastewater and also extendable for the adsorption of other heavy metals ions.

The nanoparticles have been prepared and employed as excellent adsorbents for the sequestration of heavy metal ions and hazardous impurities from the aqueous media. The surface morphological, textural and structural properties of nanoparticles have been modified, which are capable and potentially useful for the remediation of metal ions. Several metals (oxides, doped, nanocomposites of Fe, Ti, Zn, SiO2, SiC, Mo, Co, Ni, Zr, Mn, Si, S, Al, Cu, Ce, graphene, CNTs) were reported an efficient adsorbents for the removal of lead (Pb) ions from aqueous media and polluted water. The present review focuses on different kinds of nanoparticles such as metal oxides, carbon based and host supported employed for removal of Pb ions under varying experimental conditions such as pH, temperature, contact time and concentrations. The preparation strategies, physicochemical properties and adsorption are also discussed. Based on studies, it was found that the smart materials are affective adsorbents for the purification of wastewater containing Pb ions and could possibly extended for the remediation of other heavy metal ions.

Purpose. Galena and barite are the principal minerals of lead and barium respectively. Both minerals are used extensively in industries because of their distinct properties. In complex poly metallic ores, it is always desirable to produce separate mineral concentrates for subsequent metal extraction. Separation of two or more minerals from complex low-grade multi-metallic ore into commercial grade concentrates requires suitable process.Methods. This research work is centered on development a suitable process for the beneficiation of a low-grade galena-barite ore originating from Khuzdar region (Balochistan Province, Pakistan).Findings. The low-grade ore assaying 39.90% Pb and 24.64% BaSO 4 was beneficiated on bench-scale by sequential froth flotation process to recover valuable galena and barite concentrates. The important variables of froth flotation process such as feed size, pulp pH, pulp density, impeller speed, type and quantities of flotation reagents, pulp conditioning time and froth collecting time were optimized to achieve maximum recovery and grade of both concentrates. The rougher galena and barite concentrates were re-ground separately and subjected to one cleaning flotation to obtain better grade final concentrates of respective minerals. Originality.A process flow-sheet was designed in the light of this study. Practical implications.Froth flotation experiments showed that a galena concentrate containing 77.38% Pb with recovery of 90.64% and a barite concentrate assaying 90.23% BaSO 4 with recovery of 80.16% could be recovered from this ore. Both the concentrates fall in the category of metallurgical and chemical grades and are suitable for industrial applications.

Adsorption for alumina-cobalt (II) ions solution system was investigated as a function of adsorbent dose, contact time, temperature, pH of solution and initial concentration of adsorbate. The optimum conditions for removal of cobalt (II) ions were found as pH 7.5-8.5, adsorbent dose of solution 20 gl-1 , equilibrium time 90 minutes and initial concentration range 5-50 mgl-1. Pseudo-second-order kinetics was observed for adsorption of cobalt while cobalt removal process does not seem to control the intra-particle diffusion. Langmuir, Freundlich and Dubnin-Radushkevich isotherm models were applied to analyze the equilibrium isotherms for adsorption of cobalt (II) ions onto alumina. The experimental results indicated that equilibrium data follows the Langmuir model within used concentration range.

This study highlights the results of processing an indigenous low to medium grade barite oreof Duddar area, district Lasbela, Balochistan, Pakistan. The ore was characterized by x-ray diffractiontechnique. The gravity concentration and forth flotation technologies were employed to beneficiate theore in order to achieve commercial grade barite concentrate with economical recovery. The results showedthat flotation was the better method than gravity concentration to concentrate the barite mineral. A processflow sheet was designed in the light of these experiments. The flotation tests revealed that barite concentrateassaying 95.85% BaSO4 could be obtained with recovery of 82.06% from an ore containing 76.04% BaSO4.The flotation concentrate was leached to get rid of objectionable impurities. The final leached bariteconcentrate possesses 98.86% BaSO4 content and conforms to the specifications of industrial grade bariteconcentrate.