Table 1 Isotherm constants of the two-parameter and three-parameter models for the removal of Ni(II) ions by NZVI-CNS

Two-parameter models

 Langmuir model

q _m (mg/g)

70.05

0.9276

K _L (L/mg)

0.3577

SSE

203.4

RMSE

7.131

 Freundlich model

K _F [(mg/g)(L/mg)^(1/n))]

23.88

0.9901

n (g/L)

2.956

SSE

27.77

RMSE

2.635

Three-parameter models

 Redlich-Peterson model

K _RP (L/g)

64.64

0.9613

α _RP (L/mg)^(1/βRP)

2.011

β _RP

0.7487

SSE

108.7

RMSE

5.214

 Sips model

K _S (L/g)^βs

21.76

0.9848

α _s (L/mg)^(βs)

1.798

β _S

0.3806

SSE

40.31

RMSE

3.174