Which wired communication standards operate at 2km range or above?
For the 10km distance you want I think you'll be lucky to avoid repeaters (phantom powered or otherwise). 

Cable type is a big consideration. Standard RS485 cable appears to attenuate at 2dB per 100 metres and here's what Linear technology believe the max data rate to be with respect to cable length: -



At 10kbaud, 4,000 ft (1.22km) is the limit but that is for Belden 9842 cable (designed for RS485 communications). It has 2dB attenuation every 100 metres at 1MHz. 

If instead, you chose Belden 9860 you'd get only 0.66dB per 100 m at 1MHz.

A simple calculation will tell you that 9860 (not designed specifically for RS485) will give a distance of 1.22km x 3 = 3.6km for the same attenuation.

I'd also consider using FSK for transmitting the data. 

EDIT
You'd probably get double that range and if you could drive FSK with 20Vp-p you might get 10km. More volts means it goes further for the same receive signal to noise.

The graph provided by Linear tech is interesting because of it being curtailed squarely at 1.22km and 10MHz - these is not related to actual physical characteristics of the cable and, I suspect, you could reasonably predict that at 10kbaud, the transmit distance is more approaching 40,000 feet or 12.2km.