Study On The Treatment Of Cr (â…¥) Wastewater By Modified Peanut Shells And Fly Ash Adsorption Method

Chromium is listed as one of the eight biggest harm chemicals to human body, especially the hexavalent chromium Cr (VI) whose toxicity is 100 times more than Cr (III). However, there is no effective treatment method. The traditional active carbon absorption method and chemical method processing is cost higher, other methods exist their limitations. Peanut shells and fly ash as agriculture and industrial wastes, possess the advantages of source extensively and price cheap. If they can be as adsorbent treating containing Cr (VI) wastewater, it will bring tremendous environmental and economic benefit.This test adopted simulate Cr (VI) wastewater as the research object, peanut shells and fly ash as adsorbent. The influence factors on absorbent effect were studied, by the two adsorbent treating Cr (VI) wastewater experiments, including pH value, reaction time and adsorbent dosage, Cr (VI) initial concentration and temperature. The influence degree of each factor on the adsorption performance and the optimal operation parameters were analysised by orthogonal experiment. The adsorption mechanism of peanut shells and fly ash was investigated, and the adsorption isotherm equation and parameter values were confirmed.The peanut shells asorption experiment results show that when the unmodified peanut shells are in adsorption time for 400min, peanut shells dosage of 1.0 g, solution pH value 1, the Cr (VI) removal of 20mg/L wastewater reaches to 93%. The peanut shells are modified by phosphoric acid, and the parameters of peanut shells adsorption Cr (VI) concentration 30mg/L wastewater are: pH = 2, reaction time 300min, peanut shells dosing quantity 1g, reaction temperature 60℃, removal rate can reach to 90%. The influence degree order of the five factors above on peanut shells adsorption is: pH > adsorption temperature > peanut shells dosage > adsorption time > solution of initial concentration, and pH is the most important factors. The adsorption isotherm of Peanut shells adsorption on Cr (VI) is in accordance with Langmuir adsorption isotherm equation more, and saturated adsorption q⁰ is 3.016 mg/g. Low concentration Pb²⁺ dose not affect Cr (VI) adsorption by modified peanut shells, and high level Pb²⁺ is good to Cr (VI) adsorption by modified peanut shells. Na⁺ is neerly not disturbance, Cl^- is interference ions, against Cr (VI) adsorption by modified peanut shells. The penetration time of modified peanut shells is longer than 60min.The fly ash asorption experiment results show that the Cr (VI) removal by natural fly ash is only about 40%, so the fly ash need to be modified. The optimal parameters of modified fly ash preparation are: FeSO4 and Na2CO3 volume ratio 1:2, solid-liquid ratio1:10, water-bath temperature 50℃, oscillation time for 60min. When it's room temperature (about 25℃), pH=7, 1.0g modified fly ash is add to 100mL Cr (VI) wastewater whose concentration is 50mg/L, adsorption time is 30min, the removal rate of Cr(VI) can reach to 97.7%. The influence degree order of the factors above on modified fly ash Cr (VI) adsorption is: pH > fly ash dosing > adsorption temperature > adsorption time. The adsorption isotherm of modified fly ash on Cr (VI) is in accordance with Freundlich adsorption isotherm equation, saturated adsorption q⁰ is 9.737mg/g. Coexistence ions Cu²⁺, Pb²⁺ and Zn²⁺ is hardly affact Cr(VI) asorption by modified fly ash. The penetration time of modified fly ash is longer than 60min.Peanut shells and fly ash has adsorption ability on Cr (VI), after modification, adsorption performance got improved, Cr (VI) removal had some degree of improvement, adsorption processes are less vulnerable to coexist ion of interference. The modified peanut shells and fly ash has ability of adsorption Cr (VI) in wastewater, are economic and efficient absorbent.