Elsevier

Minerals Engineering

Volume 156, 1 September 2020, 106488
Minerals Engineering

Optimization of flocculation and settling parameters of tailings slurry by response surface methodology

https://doi.org/10.1016/j.mineng.2020.106488Get rights and content

Highlights

  • Flocculation and settling were studied separately by response surface methodology.

  • The effects of four parameters on three responses were investigated.

  • Multiple responses were optimized by the overall desirability function approach.

  • The optimal parameters provide information for the flocculation settling process.

Abstract

High-efficiency flocculation and settling is required for solid–liquid separation in cemented paste backfill, which is one of the best approaches for tailings management and green mining. The optimization of flocculation and settling parameters of tailings slurry was carried out by response surface methodology (RSM) with Box–Behnken design. The solid fraction, flocculant dosage, flocculant concentration, and shear rate were selected as the factor. Likewise, the maximum square-weighted mean chord length of tailings floc, initial settling rate of the suspension-supernate interface, and turbidity of supernate were selected to characterize the flocculation and settling process. For individual response, a quadratic polynomial regression model was proposed and optimal parameters were achieved by RSM. Multiple response optimization by the overall desirability function approach was applied successfully to estimate the optimal parameters, i.e., solid fraction of 10.29%, flocculant dosage of 25%, flocculant concentration of 0.15%, and shear rate of 51.60 s−1. The validation experiments demonstrated that the Box–Behnken design in RSM is an appropriate and powerful approach for the optimization of flocculation and settling parameters of Nickel tailings slurry. More importantly, the optimal parameters achieved provide valuable information for the flocculation settling process of unclassified Nickel tailings slurry in Jinchuan Nickel Deposit, which will contribute to tailings management and water recycling, avoiding air pollution, water pollution, and soil pollution in mine.

Introduction

Millions of tons of mineral tailings are produced annually, which leads to safety and environmental issues, including air pollution, water pollution, and soil pollution (Edraki et al., 2014, Wang et al., 2014). Cemented paste backfill (CPB) has been one of the best approaches for tailings management and green mining (Qi and Fourie, 2019, Yin et al., 2020). To improve the solid–liquid separation performance in CPB, flocculant, especially the polymer flocculant, is widely applied for tailings management (Lu et al., 2016, Meggyes and Debreczeni, 2006) and water recovery in mine (Jiao et al., 2020, Rooney et al., 2016). With polymer-bridging flocculation, fine solid particles can grow to bigger fast-settling flocs (Concha, 2014).

High settling rate, low-turbidity overflow, and high-concentration underflow are the main requirements for efficient dewatering in a thickener or clarifier (Joseph-Soly et al., 2016). Most attention has been paid to the influence of flocculation conditions on settling rate and/or underflow concentration. These flocculation conditions include flocculant type and flocculant dosage (Dwari et al., 2018, Tanguay et al., 2014, Yang et al., 2019), primary particle size (Grabsch et al., 2020, Motta et al., 2018), solid fraction of slurry (Heath et al., 2006, Wu et al., 2016), chemical composition (Botha and Soares, 2015, Nguyen et al., 2007), acidity (pH) (Konduri and Fatehi, 2017, Li et al., 2016), fluid shear rate (Betancourt et al., 2020, Carissimi and Rubio, 2015, del Río et al., 2019, Wang et al., 2018), etc. However, less emphasis was placed on the tailings floc characteristics, as well as the relationship between the floc and tailings dewatering. Fawell and his team (Benn et al., 2018, Fawell et al., 2019) investigated the tailings flocculation and flocculated slurry sedimentation, and promoted gravity thickener feedwell design and operation.

Inspired by the above works, we investigated the influence of solid fraction, flocculant dosage and concentration, and shear rate on floc size, initial settling rate of suspension-supernate interface, and the turbidity of supernate by response surface methodology (RSM). The flocculation process and settling process were studied separately. The optimal parameters of flocculation and settling were obtained, which will provide a reference for improving the flocculation settling process of unclassified Nickel tailings slurry in the CPB in Jinchuan Nickel Deposit, a world-renowned multi-metal-associated sulfide deposit. (Yang, 2017).

Section snippets

Tailings and flocculant

The tailings were sampled from the Jinchuan Nickel Deposit located in the northwest of China. The specific gravity (density) of copper tailings measured by the water pycnometer test method is 2.785 g cm−3. The particle size distribution (PSD) of tailings was analyzed by laser diffraction (TopSizer, OMEC, China). The PSD is shown in Fig. 1.

Based on the previous study (Wu et al., 2020), Magnafloc 5250 obtained from BASF, with a molecular mass of 20 million Dalton has a good flocculation

Overall performance

The dynamic variation of SWMCL and suspension-supernate interface height with time are shown in Figs. 3 and 4, respectively.

From Fig. 3, it can be found that SWMCL in each run increased rapidly to the peak, and then decreased gradually with flocculation time until it reached a stable state. The peak value is the SWMCLmax of each run. From the initial linear part of each setting curve in Fig. 4, the absolute value of slope calculated was the ISR of each run (Lu et al., 2016). The designed 29

Conclusions and future work

In this work, the optimization of flocculation and settling parameters of tailings slurry was carried out. Response surface methodology (RSM) with Box–Behnken design (BBD) was employed to investigate the influences of solid fraction (SF), flocculant dosage (FD), flocculant concentration (FC), and shear rate (G) on the maximum square-weighted mean chord length (SWMCLmax) of tailings floc, initial settling rate (ISR) of the suspension-supernate interface, and turbidity (T) of supernate. Based on

CRediT authorship contribution statement

Aixiang Wu: Conceptualization, Supervision, Methodology, Funding acquisition, Writing - original draft, Writing - review & editing. Zhuen Ruan: Methodology, Investigation, Formal analysis, Software, Validation, Writing - original draft, Writing - review & editing. Raimund Bürger: Validation, Writing - original draft, Writing - review & editing, Funding acquisition. Shenghua Yin: Resources, Writing - review & editing. Jiandong Wang: Investigation, Software, Writing - original draft. Yong Wang:

Acknowledgment

A. W., Z. R., S. Y. and J. W. acknowledge financial support by the Key Program of National Natural Science Foundation of China (No. 51834001). Z. R. and Y. W. acknowledge financial support by the National Natural Science Foundation of China (No. 51804015) and the Fundamental Research Funds for the Central Universities (No. 06500121). R. B. acknowledges support by Fondecyt project 1170473; CONICYT/PIA/AFB170001; CRHIAM, Project ANID/FONDAP/15130015; and by the INRIA Associated Team “Efficient

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