Direct
sulfidation using a high concentration of H2S
(HC-H2S) has shown potential for heavy metals removal in
various acidic effluents. However, the lack of a smooth method for
producing HC-H2S is a critical challenge. Herein, a novel
short-process hydrolysis method was developed for the on-site production
of HC-H2S. Near-perfect 100% efficiency and selectivity
were obtained via CS2 hydrolysis over the ZrO2-based catalyst. Meanwhile, no apparent residual sulfur/sulfate poisoning
was detected, which guaranteed long-term operation. The coexistence
of CO2 in the products had a negligible effect on the complete
hydrolysis of CS2. H2S production followed a
sequential hydrolysis pathway, with the reactions for CS2 adsorption and dissociation being the rate-determining steps. The
energy balance indicated that HC-H2S production was a mildly
exothermic reaction, and the heat energy could be maintained at self-balance
with approximately 80% heat recovery. The batch sulfidation efficiencies
for As(III), Hg(II), Pb(II), and Cd(II) removal were over 99.9%, following
the solubilities (K
sp) of the corresponding
metal sulfides. CO2 in the mixed gas produced by CS2 hydrolysis did not affect heavy metals sulfidation due to
the presence of abundant H+. Finally, a pilot-scale experiment
successfully demonstrated the practical effects. Therefore, this novel
on-site HC-H2S production method adequately achieved heavy
metals removal requirements in acidic effluents.
Pretreatments for delignification are necessarily required for the enzymatic saccharification of lignocellulosic biomass. However, in current literature various pretreatment approaches have been applied to same kinds of biomass. In order to find the optimum pretreatments for biomass with various lignin contents, a quantitative comparison has been made on the delignification performance of 15 categories of pretreatments in this study. In total, 1729 series of biomass, cellulose, hemicellulose, and lignin recovery data were collected from 214 relevant studies. The box-plots and Cate-Nelson-like graphs were applied for the analysis. The results showed that among the 15 pretreatment categories, alkali, oxidation, organic solvent, and multiple-step pretreatments worked better to remove more lignin while recover more cellulose. Moreover, alkali pretreatments tended to more evidently increase saccharification efficiency by about five folds on average than the other three pretreatments.
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