Efficiency of extremophilic microbial mats for removing of Pb ( II ) , 1 Cu ( II ) and Ni ( II ) ions from aqueous solutions 2

Two different extremophilic films were used as natural biosorbents to remove Cu(II), Ni(II) 12 and Pb(II) from aqueous solution. Surface area, scanning electron microscope imaging and 13 Fourier transformation infrared were used to characterize the surface of biosorbents. The 14 results indicated high affinity of biosorbents to remove Pb(II) Cu(II) and Ni(II) with 15 adsorption ratio ranged between 73.6% to 100% for both two biosorbent. The two biosorbents 16 success to remove the metal ions from the aqueous mixture in the order of Pb(II) > Cu(II) > 17 Ni(II). The maximum removal ratios of metal ions were achieved at pH = 6, 150 min contact 18 time, 2.5 g/L biosorbent dose and 50 mg/L metal ions. The isothermal studies showed that 19 both Langmuir and Freundlich models well expressed the adsorption process. Kinetically, the 20 pseudo-second order reaction well express the type of reaction than pseud-first order reaction. 21


24
In recent decades, the humanity has realized the need to conserve the surrounding 25 environment and different habitants. Pollution, especially with heavy metals, affects the life 26 of the planet either directly or indirectly. The toxic pollutants are generating during different 27 stages in industrial processes (Landa-Acuña et al. 2020) and mining (Beltrán-Pineda and 28 Gómez-Rodríguez, 2016). These pollutants tend to accumulate or transport into the 29 environment, providing an alarm issues of toxic products (Rai and Tripathi 2007). Some 30 heavy metals e.g. Cd, Pb, Hg, As, Ni and Cr etc. are found in the industrial wastes causing 31 serious problems to aquatic environment due to their accumulation, non-degradation nature 32 and their long persistence in the tissues (Gupta et al. 2016). Owing to exacerbation toxic 33 metals problems in the environment, the researchers stepped up their efforts to develop an 34 eco-friendly, low cost and clean techniques to overcome this serious situation. Bioremediation 35 hydrocarbons and heavy metals (Kumar and Kundu 2020) due to their high growth rate that 48 giving high surface area which permits high adsorptive capacity for heavy metals binding 49 (Ahad et al. 2017). Many scientists reported excellent biosorption removal efficiency for several 59 cyanobacterial strains. Oscillatoria anguistissima had high removal efficiency for Zn 60 biosorption (641 mg/g of dry weight) (Ahuja et al. 1999 Teller (BET) method using a Coulter SA3100 with outgas of 15 min at 150 ºC (Brunauer et 95 al. 1938). Pore diameter, pore volume and micropore surface area were determined by the 96 Barrett-Joyner-Halenda (BJH) method (Barrett et al. 1951). Scanning electron microscope 97 (JEM-2100, JEOL, Tokyo Japan) at an acceleration voltage of 200 kV was used for scanning 98 electron microscope imaging (SEM) and energy dispersive X-ray spectroscopy (EDX). The 99 Fourier transform infrared spectra (FT-IR) were measured before and after metal adsorption 100 using spectrum spectrometer (6700 FTIR, Nicolet, America). The samples were ground with 101 KBr (1:100) the measurements were taken within the range of 400-4000 cm -1 . 102 Surface areas of biosorbents were measured to illustrate their capacity to adsorb metals 127 (Table 1). Biosorbent 2 has higher surface area than microbial film from biosorbent 1. 128

Scanning electron microscope (SEM) 131
The morphological differences between surfaces of biosorbents before and after 132 adsorption of Cu(II), Ni(II) and Pb(II) ions were detected using scanning electron microscope 133 (SEM). Figure (

b)
The biosorption of Cu(II), Ni(II) and Pb(II) onto the surface of biosorbent 1 and biosorbent 2 244 are shown in Fig (5 A&B). The results showed that the uptake of Cu and Pb by two 245 biosorbents was rapidly took placed reached to about 70% during first 30 min while the rate 246 of Ni is lower (45%), the rate became slower by increasing the time till reached the maximum 247 removal efficiency after 150 min then the rate tend to be steady (Figure 5 A&B).

Effect of biosorbent dose 261
In general, the increased in microbial biomass is accompanied with increase of 262 adsorption process of metals ions due to availability of high surface area provides more and 263 more active binding sites (Michalak et al. 2013). Thereby, studying of biosorbents dose 264 variation regarded as an important factor affects the biosorption process (  The maximum removal ratios of biosorbent 2 reached to 95.9 %, 80.3% and 72.4% for Pb, Cu 272 and Ni were obtained ( Figure 6B). 273  where: qmax (mg/g) the maximum adsorption capacity, qe is metals ions 297 concentrations adsorbed at equilibrium (mg/g), b (L/mg) Langmuir constant. 298

Effect of Initial Metal Concentration
Langmuir separation constant (RL) was calculated as follow: 299 Where Ci is initial metal ions concentration (mg/L); b is the Langmuir constant. 301 Separation factor (RL) value determine Langmuir isotherm type; if RL = 0 (irreversible), L = 302 1 (linear), L > 1 (unfavorable), or 0 < L < 1 (favorable) (McKay et al. 1982). Where: qe is the adsorbed metal amount (mg/g), Ce is the equilibrium adsorbate 311 concentration in mg/L, Kf is the adsorbent capacity and n is the adsorption intensity. 312

Calculated constants of Langmuir and Freundlich for the biosorption of Pb(II), Cu(II) 313
and Ni(II) onto the surface of used biosorbents are found in Table (4) and graphically 314 represented in Figures (8 & 9). The results showed that both Langmuir and Freundlich models 315 are well-fitting to describe the isothermal biosorption type with R 2 > 0.95. A narrow 316 difference between the adsorption capacities of both biosorbents was observed. L range of 0 317 < L < 1 indicated that favorable adsorption of Pb(II), Cu(II) and Ni(II) was achieved (Table  318 4). The lower values of (< 1) for studied metals ions revealed that the adsorption is a 319 chemical adsorption process (Desta 2013). 320 321

Kinetics studies 358
Studies of biosorption kinetic is an important factor to evaluate the biosorption 359 efficiency (Moghadam et al. 2013). Thus, pseudo-first order and pseudo-second order models 360 were used to illustrate the kinetics biosorption of Pb(II), Cu(II) and Ni(II) onto surface of the 361 two cyanobacterial biosorbents.  Where: qt is adsorbed metal ions (mg/g) at time t, qe is the amount of adsorbed metal ions (mg/g) 375 at equilibrium, k2 (mg/g.min -1 ) is the constant of pseudo-second order reaction

376
The kinetic constants and the linear plots of the pseudo-first and the pseudo-second 377 order reactions are given in Table 5 and presented graphically in Figs 10 & 11. In accordance 378 of calculated constants for both biosorbents, we can conclude that biosorption of studied 379 metals followed the pseudo-second order reaction. The recorded qe ranged between 19.72 -380 26.3 and 18.97 -24.1 mg/g for the two biosorbents with R 2 exceed than 0.99. 381 382

416
Two different microbial mats inhabit extreme habitats collected from hot spring 417 (biosorbent 1) and from cold spring (biosorbent 2) and used these mats to remove Pb(II),