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Mar 26, 2018 - Removal of Arsenic from Strongly Acidic Wastewater Using Phosphorus Pentasulfide As Precipitant: UV-Light Promoted Sulfuration Reaction...
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Removal of arsenic from strongly acidic wastewater using phosphorus pentasulfide as precipitant: UV-light promoted sulfuration reaction and particle aggregation Xianjia Peng, Jingyi Chen, Linghao Kong, and Xingyun Hu Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 26 Mar 2018 Downloaded from http://pubs.acs.org on March 26, 2018

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Environmental Science & Technology

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Removal of arsenic from strongly acidic wastewater using

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phosphorus pentasulfide as precipitant: UV-light promoted

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sulfuration reaction and particle aggregation

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Xianjia Peng1,2,3, Jingyi Chen1,2,3, Linghao Kong*,1,2, Xingyun Hu1,2

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1. National Engineering Laboratory for Industrial Wastewater Treatment, Research Center

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for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

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2. Beijing Key Laboratory of Industrial Wastewater Treatment and Resource Recovery,

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Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing

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100085, China

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3. University of Chinese Academy of Sciences, Beijing 100049, China

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* Corresponding author:

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Linghao Kong

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Tel: +86-10-6284 9198

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Fax: +86-10-6284 9198

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E-mail: [email protected]

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ABSTRACT

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Strongly acidic wastewater (H2SO4) with a high arsenic concentration is produced by many

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industries. The removal of arsenic by traditional sulfide (e.g. Na2S, FeS) from strongly

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acidic wastewater introduces cations (Na+ and Fe2+) to the solution, which may prevent the

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recycle of acid. In this study, a new sulfuration agent, phosphorus pentasulfide (P2S5) was

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employed, and its feasibility in arsenic removal from strongly acidic wastewater was

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investigated. In the dark, As(III) was efficiently removed, but the removal rate of As(V) was

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rather slow, which was the crucial defect for this method. We found that this defect can be

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efficiently overcome by UV irradiation through accelerating the formation and

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transformation of an intermediate species, monothioarsenate (H3AsO3S) in the As(V)

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removal process. In addition, the hydrolysis of P2S5 was enhanced under UV irradiation,

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which resulted in the increase of the arsenic removal efficiencies. Besides, the aggregation

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of the formed particles was also promoted. Different from FeS and Na2S, P2S5 introduces

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H3PO4 instead of cations to the solution, which can facilitate the recycle and reuse of arsenic

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and acid in strongly acidic wastewater.

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Introduction

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Large quantities of strongly acidic wastewater with high arsenic concentration is

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produced by nonferrous metal smelting industry, mineral processing industry, and sulfuric

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acid production industry, etc. For instance, in a typical sulfuric acid production process,

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pyrite ores or sulfide concentrates are roasted in fluidized beds to generate

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arsenic-containing SO2. The gases are cleaned and thus strongly acidic wastewater with high

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concentration of arsenic is produced in this process.1

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The removal of arsenic from strongly acidic wastewater remains difficult. Current

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technologies available for arsenic removal from acidic water include adsorption,

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co-precipitation, bio-removal, etc. Adsorbents such as TiO2,2 iron (hydro)oxide modified

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zeolite 3 and co-precipitation reagents, such as Fe(III) 4-6 have been utilized for the treatment

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of arsenic-containing acidic wastewater. However, a weak acidic or neutral condition is

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required in these methods, which means that a neutralization process using Na2CO3, sodium

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hydroxide, ammonia and other alkaline reagents is necessary before the treatment. In these

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processes, however, acid is lost irreversibly and the acidic wastewater is transformed to

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wastewater with high concentration of salt which may still pose a threat to the environment.

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Bioprocesses have also been developed for arsenic-containing acidic wastewater treatment

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and high removal efficiencies of arsenic have been obtained under weak acidic conditions.

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7-12

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applied under mildly acidic conditions (pH range of 2-6),7-12 because the microbial activity

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can be strongly inhibited by strongly acidic conditions (pH