How Could Superman Lift the Oceanliner Out of the Water While He Was Surrounded by Kryptonite?

The 'coating' is the surrounding geology (including matter from the seabed) but even before he is directly exposed to the Kryptonite infused portions of the crystal continent, it is apparent to the viewers that it may already be having a effect as he struggles to lift it all into the air.

Although unaware that his injury has not been completely dealt with (there is still a tiny shard of Kryptonite in the injury inflicted by Luthor) Superman gives himself the best opportunity to tackle this by first soaring up into the upper atmosphere to regain as much strength as possible (derived from his direct exposure to the Sun), before plunging back through the foundations of the continent / island / whatever to separate and lift it from the surrounding seabed.

Although he struggles for the reasons stated above, he still manages to lift it thanks to the surge of energy he had just absorbed and due to the buffer created by the 'coating' you describe of surrounding mineral, not becoming directly exposed to the Kryptonite until they are almost in space.

Although he is successful (rocket science and escape velocities be dammed) he still only barely achieves his goal and as such it goes without saying that it costs him. The effort causes him to loose consciousness for an unspecified amount of time and it is only after the removal of the final Kryptonite shard and his subsequent rest and recovery that sees him back on his feet and up, up and on his away again.

Close call for Superman that one and while like many comic book plot lines the details make about as much sense as a chocolate teapot, I believe that this best explains his achievement and its consequences based on the internal logic of the film.