Adsorption Of Pb(â…¡) And Ni(â…¡) From Water On Walunt Shell-based Adsorbent

Heavy metals are produced among the frequented industrial activities, it must be seriouswhen the water contaminated by toxic and no-biodegradable metal ions discharged optionally.The organic agriculture residues are used removing heavy metals from wastewater has causedextensively attention, mainly because of its low cost, high efficiency in removing heavymetals and environmental friendly. After the course of crushing, screening and washing,xinjiang walnut shell are made into adsorbent in this paper. The static adsorption of Pb2+andNi2+by walnut shell are conducted the parameters with high efficiency; the analysis ofdynamics, isothermal model, scanning electron microscope(SEM) and Fourier transforminfrared spectrometry (FTIR) are speculated the adsorption mechanism, all above are toprovide reliable data on adsorption of Pb2+and Ni2+by walnut shell for engineering practice.The result show that the removel rate of Pb2+, Ni2+increases at first then remain untilwhen the adsorption process reach to the equilibrium at120min and360min, respectively.The initial concentration of Pb2+, Ni2+is20mg/L,10mg/L, the optimal solution pH foradsorption is5.5and6.0, the optimal particle size of walnut shell is1.6-2.5mm, the mass ofadsorbent is1.2g and2.0g per100mL simulated solutions, all above leads to the removal rateof Pb2+, Ni2+reached maximum.0.1mol/L HNO3can be used to desorb the laden Pb2+, Ni2+onthe walnut shell. the removel rate of Pb2+, Ni2+declines12.6%and6.4%respectively as theadsorbent recycle five times; the removel rate of Pb2+declines5.6%as the adsorbent reuse sixtimes, after three times reusing, the residual concentration of Pb2+is0.98mg/L, it is achievesComprehensive Emissions Standard for Sewage (GB8978-1996), the industrial reused numberof walnut shell should contral in three times.The double component test show that the adsorption capacity of Ni2+declined sharplythan Pb2+when other metal ions exists, the relationship of Pb2+, Ni2+is competitive adsorption,mainly because the hydration energy of Pb2+is smaller than Ni2+, that is beneficial to theunites between adsorbent and metal ions in solution. The prior adsorption further prove thatadsorbent had a better affinity for Pb2+.The pseudo-second-order model is fitted to describe the adsorption of Pb2+and Ni2+, thecorrelation is all above0.99, the max adsorption capacity of Pb2+and Ni2+is3.903mg/g and0.687mg/g, the laboratorial adsorption capacity approach the fitting date, it is shown thatadsorption rate for the two metal ions in proportion to the square of the driving force, and theadsorption rate was controlled by chemical adsorption; the equilibrium concentration ofadsorption fit well with Langmuir isotherm equation, the adsorption of Pb2+and Ni2+ismonolayer adsorption. Scanning electron microscopy (SEM), FTIR analysis of walnut shell reveal that theadsorption mechanism may be the one or two, perhaps the combined action of three, that aresurface complexation, ion exchange and inorganic micro precipitation, mainly, O-H (acid) andC-H are involved in the adsorption of Pb2+, Ni2+, also includes the C=O (amide) and C=C.The reaction should occur chemical adsorption and physical adsorption to Pb2+, Ni2+.