Akhtar Mubeena, Bhanger M I, Iqbal Shahid, Hasany S Moosa
National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro-76080, Pakistan.
J Hazard Mater. 2006 Jan 16;128(1):44-52. doi: 10.1016/j.jhazmat.2005.07.025. Epub 2005 Aug 26.
The sorption potential of chemically and thermally treated rice husk (RHT) for the removal of 2,4-dichlorophenol (DCP) from aqueous solutions has been investigated. Sorption of DCP by rice husk was observed over a wide pH range of 1-10. The effect of contact time between liquid and solid phases, sorbent dose, pH, concentration of sorbate and temperature on the sorption of DCP onto rice husk has been studied. The pore area and average pore diameter of RHT by BET method are calculated to be 17+/-0.6 m2g-1 and 51.3+/-1.5 nm, respectively. Maximum sorption (98+/-1.2%) was achieved for RHT from 6.1x10(-5) moldm(-3) of sorbate solution using 0.1g of rice husk for 10 min agitation time at pH 6 and 303K, which is comparable to activated carbon commercial (ACC) 96.6+/-1.2%, but significantly higher than chemically treated rice husk (RHCT) 65+/-1.6% and rice husk untreated (RHUT) 41+/-2.3%. The sorption data obtained at optimized conditions was subjected to Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. Sorption intensity 1/n (0.31+/-0.01) and sorption capacity multilayer C(m) (12.0+/-1.6 mmolg(-1)) have been evaluated using Freundlich sorption isotherm, whereas the values of sorption capacity monolayer Q (0.96+/-0.03 mmolg(-1)) and binding energy, b, (4.5+/-1.0)x10(4)dm(3)mol(-1) have been estimated by Langmuir isotherm. The Langmuir constant, b, was also used to calculate the dimensionless factor, R(L), in the concentration range (0.6-6.1)x10(-4) moldm(-3), suggesting greater sorption at low concentration. D-R sorption isotherm was employed to calculate sorption capacity X(m) (2.5+/-0.07 mmolg(-1)) and sorption energy E (14.7+/-0.13 kJmol(-1)). Lagergren and Morris-Weber equations were employed to study kinetics of sorption process using 0.2g of RHT, 25 cm(3) of 0.61x10(-4)moldm(-3) sorbate concentration at pH 6, giving values of first-order rate constant, k, and rate constant of intraparticle transport, R(id), (0.48+/-0.04 min(-1) and 6.8+/-0.8 nmolg(-1)min(-1/2), respectively) at 0.61x10(-4)moldm(-3) solution concentration of DCP, 0.1g RHT, pH 6 and 2-10min of agitation time. For thermodynamic studies, sorption potential was examined over temperature range 283-323 K by employing 6.1x10(-4)moldm(-3) solution concentration of DCP, 0.1g RHT at pH 6 and 10 min of agitation time and values of DeltaH (-25+/-1 kJmol(-1)), DeltaS (-61+/-4 Jmol(-1)K(-1)) and DeltaG(303K) (-7.1+/-0.09 kJmol(-1)) were computed. The negative values of enthalpy, entropy, and free energy suggest that the sorption is exothermic, stable, and spontaneous in nature.
研究了化学和热处理稻壳（RHT）从水溶液中去除2,4 - 二氯苯酚（DCP）的吸附潜力。在1 - 10的宽pH范围内观察到稻壳对DCP的吸附。研究了液固相接触时间、吸附剂剂量、pH、吸附质浓度和温度对DCP在稻壳上吸附的影响。通过BET法计算得出RHT的孔面积和平均孔径分别为17±0.6 m²g⁻¹和51.3±1.5 nm。使用0.1g稻壳，在pH 6和303K下搅拌10分钟，从6.1×10⁻⁵ moldm⁻³的吸附质溶液中，RHT实现了最大吸附量（98±1.2%），这与商业活性炭（ACC）的96.6±1.2%相当，但显著高于化学处理稻壳（RHCT）的65±1.6%和未处理稻壳（RHUT）的41±2.3%。在优化条件下获得的吸附数据采用Freundlich、Langmuir和Dubinin - Radushkevich（D - R）等温线进行处理。使用Freundlich吸附等温线评估了吸附强度1/n（0.31±0.01）和多层吸附容量C(m)（12.0±1.6 mmol g⁻¹），而通过Langmuir等温线估计了单层吸附容量Q（0.96±0.03 mmol g⁻¹）和结合能b（4.5±1.0）×10⁴ dm³ mol⁻¹。Langmuir常数b还用于计算浓度范围为（0.6 - 6.1）×10⁻⁴ moldm⁻³内的无量纲因子R(L)，表明在低浓度下吸附作用更强。采用D - R吸附等温线计算吸附容量X(m)（2.5±0.07 mmol g⁻¹）和吸附能E（14.7±0.13 kJ mol⁻¹）。使用0.2g RHT、25 cm³ 0.61×10⁻⁴ moldm⁻³的吸附质浓度、pH 6，采用Lagergren和Morris - Weber方程研究吸附过程的动力学，在DCP溶液浓度为0.61×10⁻⁴ moldm⁻³、0.1g RHT、pH 6和搅拌时间为2 - 10分钟时，得到一级速率常数k和颗粒内扩散速率常数R(id)分别为（0.48±0.04 min⁻¹和6.8±0.8 nmol g⁻¹ min⁻¹/²）。对于热力学研究，采用6.1×10⁻⁴ moldm⁻³的DCP溶液浓度、0.1g RHT、pH 6和搅拌10分钟，在283 - 323 K的温度范围内研究吸附潜力，并计算出ΔH（-25±1 kJ mol⁻¹）、ΔS（-61±4 J mol⁻¹ K⁻¹）和ΔG(303K)（-7.1±0.09 kJ mol⁻¹）。焓、熵和自由能的负值表明吸附是放热的、稳定的且本质上是自发的。
